diff --git a/src/HotChocolate/Core/src/Validation/DocumentValidatorContext.cs b/src/HotChocolate/Core/src/Validation/DocumentValidatorContext.cs
index fe2a3c3f599..e5588b5520f 100644
--- a/src/HotChocolate/Core/src/Validation/DocumentValidatorContext.cs
+++ b/src/HotChocolate/Core/src/Validation/DocumentValidatorContext.cs
@@ -61,6 +61,9 @@ public IOutputType NonNullString
         public IDictionary<SelectionSetNode, IList<FieldInfo>> FieldSets { get; } =
             new Dictionary<SelectionSetNode, IList<FieldInfo>>();
 
+        public ISet<(FieldNode, FieldNode)> FieldTuples { get; } = 
+            new HashSet<(FieldNode, FieldNode)>();
+
         public ISet<string> VisitedFragments { get; } = new HashSet<string>();
 
         public IDictionary<string, object> VariableValues { get; } =
@@ -130,6 +133,7 @@ public void Clear()
             Path.Clear();
             SelectionSets.Clear();
             FieldSets.Clear();
+            FieldTuples.Clear();
             VisitedFragments.Clear();
             VariableValues.Clear();
             Variables.Clear();
diff --git a/src/HotChocolate/Core/src/Validation/IDocumentValidatorContext.cs b/src/HotChocolate/Core/src/Validation/IDocumentValidatorContext.cs
index 2fcb7d5b2e2..3cb3c6516c5 100644
--- a/src/HotChocolate/Core/src/Validation/IDocumentValidatorContext.cs
+++ b/src/HotChocolate/Core/src/Validation/IDocumentValidatorContext.cs
@@ -35,6 +35,11 @@ public interface IDocumentValidatorContext : ISyntaxVisitorContext
         /// A dictionary to store field infos per selection set.
         /// </summary>
         IDictionary<SelectionSetNode, IList<FieldInfo>> FieldSets { get; }
+        
+        /// <summary>
+        /// A set of field tuples.
+        /// </summary>
+        ISet<(FieldNode, FieldNode)> FieldTuples { get; }
 
         /// <summary>
         /// Gets a set of already visited fragment names.
diff --git a/src/HotChocolate/Core/src/Validation/Rules/FieldVisitor.cs b/src/HotChocolate/Core/src/Validation/Rules/FieldVisitor.cs
index 51e8391135d..848125a12f5 100644
--- a/src/HotChocolate/Core/src/Validation/Rules/FieldVisitor.cs
+++ b/src/HotChocolate/Core/src/Validation/Rules/FieldVisitor.cs
@@ -42,7 +42,10 @@ internal sealed class FieldVisitor : TypeDocumentValidatorVisitor
         {
             if (context.FieldSets.Count > 0)
             {
-                TryMergeFieldsInSet(context, context.FieldSets[node.SelectionSet]);
+                foreach (SelectionSetNode selectionSet in context.FieldSets.Keys)
+                {
+                    TryMergeFieldsInSet(context, context.FieldSets[selectionSet]);
+                }
             }
 
             if (node.SelectionSet.Selections.Count == 0)
@@ -75,7 +78,7 @@ internal sealed class FieldVisitor : TypeDocumentValidatorVisitor
             if (context.Types.TryPeek(out IType type) &&
                 type.NamedType() is IComplexOutputType ct)
             {
-                if (ct.Fields.TryGetField(node.Name.Value, out IOutputField of))
+                if (ct.Fields.TryGetField(node.Name.Value, out IOutputField? of))
                 {
                     fields.Add(new FieldInfo(context.Types.Peek(), of.Type, node));
 
@@ -155,6 +158,7 @@ internal sealed class FieldVisitor : TypeDocumentValidatorVisitor
                     context.SelectionSets.Pop();
                 }
             }
+
             return Continue;
         }
 
@@ -235,14 +239,14 @@ private static bool IsTypeNameField(NameString fieldName)
                                     {
                                         TryMergeFieldsInSet(context, fieldA, fieldB);
                                     }
-                                    else
+                                    else if(context.FieldTuples.Add((fieldA.Field, fieldB.Field)))
                                     {
                                         context.Errors.Add(
                                             context.FieldsAreNotMergable(fieldA, fieldB));
                                     }
                                 }
                             }
-                            else
+                            else if(context.FieldTuples.Add((fieldA.Field, fieldB.Field)))
                             {
                                 context.Errors.Add(context.FieldsAreNotMergable(fieldA, fieldB));
                             }
diff --git a/src/HotChocolate/Core/test/Validation.Tests/FieldSelectionMergingRuleTests.cs b/src/HotChocolate/Core/test/Validation.Tests/FieldSelectionMergingRuleTests.cs
index 061a5a2a878..7cb37021b91 100644
--- a/src/HotChocolate/Core/test/Validation.Tests/FieldSelectionMergingRuleTests.cs
+++ b/src/HotChocolate/Core/test/Validation.Tests/FieldSelectionMergingRuleTests.cs
@@ -1,4 +1,5 @@
 using ChilliCream.Testing;
+using HotChocolate.Types;
 using Microsoft.Extensions.DependencyInjection;
 using Xunit;
 
@@ -309,7 +310,6 @@ ... FooLevel2
                 t.Message));
         }
 
-
         [Fact]
         public void ShortHandQueryWithDupMergableFieldInSecondLevelFragment()
         {
@@ -368,9 +368,15 @@ ... interfaceFieldSelection
         }
 
         [Fact]
-        public void TypeNameFieldOnObjectIsMergable()
+        public void TypeNameFieldOnObjectIsMergeable()
         {
             ExpectValid(@"
+                {
+                    catOrDog {
+                        ... interfaceFieldSelection
+                    }
+                }
+
                 fragment interfaceFieldSelection on Cat {
                     __typename
                     __typename
@@ -383,5 +389,763 @@ public void InvalidFieldsShouldNotRaiseValidationError()
         {
             ExpectValid(FileResource.Open("InvalidIntrospectionQuery.graphql"));
         }
+
+        [Fact]
+        public void UniqueFields()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... uniqueFields
+                    }
+                }
+
+                fragment uniqueFields on Dog {
+                    name
+                    nickname
+                }
+            ");
+        }
+
+        [Fact]
+        public void IdenticalFields()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... mergeIdenticalFields
+                    }
+                }
+
+                fragment mergeIdenticalFields on Dog {
+                    name
+                    name
+                }
+            ");
+        }
+
+        [Fact]
+        public void IdenticalFieldsWithIdenticalArgs()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... mergeIdenticalFieldsWithIdenticalArgs
+                    }
+                }
+
+                fragment mergeIdenticalFieldsWithIdenticalArgs on Dog {
+                    doesKnowCommand(dogCommand: SIT)
+                    doesKnowCommand(dogCommand: SIT)
+                }
+            ");
+        }
+
+        [Fact]
+        public void DifferentArgsWithDifferentAliases()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... differentArgsWithDifferentAliases
+                    }
+                }
+
+                fragment differentArgsWithDifferentAliases on Dog {
+                    knowsSit: doesKnowCommand(dogCommand: SIT)
+                    knowsDown: doesKnowCommand(dogCommand: DOWN)
+                }
+            ");
+        }
+
+        [Fact]
+        public void DifferentDirectivesWithDifferentAliases()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... differentDirectivesWithDifferentAliases
+                    }
+                }
+
+                fragment differentDirectivesWithDifferentAliases on Dog {
+                    nameIfTrue: name @include(if: true)
+                    nameIfFalse: name @include(if: false)
+                }
+            ");
+        }
+
+        [Fact]
+        public void DifferentSkipIncludeDirectivesAccepted()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... differentDirectivesWithDifferentAliases
+                    }
+                }
+
+                fragment differentDirectivesWithDifferentAliases on Dog {
+                    name @include(if: true)
+                    name @include(if: false)
+                }
+            ");
+        }
+
+        [Fact]
+        public void SameAliasesWithDifferentFieldTargets()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... sameAliasesWithDifferentFieldTargets
+                    }
+                }
+
+                fragment sameAliasesWithDifferentFieldTargets on Dog {
+                    fido: name
+                    fido: nickname
+                }
+            ");
+        }
+
+        [Fact]
+        public void SameAliasesAllowedOnNonOverlappingFields()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... sameAliasesWithDifferentFieldTargets
+                    }
+                }
+
+                fragment sameAliasesWithDifferentFieldTargets on Pet {
+                    ... on Dog {
+                        name
+                    }
+                    ... on Cat {
+                        name: nickname
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void AliasMaskingDirectFieldAccess()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... aliasMaskingDirectFieldAccess
+                    }
+                }
+
+                fragment aliasMaskingDirectFieldAccess on Dog {
+                    name: nickname
+                    name
+                }
+            ");
+        }
+
+        [Fact]
+        public void DifferentArgsSecondAddsAnArgument()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... conflictingArgs
+                    }
+                }
+
+                fragment conflictingArgs on Dog {
+                    doesKnowCommand
+                    doesKnowCommand(dogCommand: HEEL)
+                }
+            ");
+        }
+
+        [Fact]
+        public void DifferentArgsSecondMissingAnArgument()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... conflictingArgs
+                    }
+                }
+
+                fragment conflictingArgs on Dog {
+                    doesKnowCommand(dogCommand: SIT)
+                    doesKnowCommand
+                }
+            ");
+        }
+
+        [Fact]
+        public void ConflictingArgValues()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... conflictingArgs
+                    }
+                }
+
+                fragment conflictingArgs on Dog {
+                    doesKnowCommand(dogCommand: SIT)
+                    doesKnowCommand(dogCommand: HEEL)
+                }
+            ");
+        }
+
+        [Fact]
+        public void ConflictingArgNames()
+        {
+            ExpectErrors(@"
+                {
+                    catOrDog {
+                        ... conflictingArgs
+                    }
+                }
+
+                fragment conflictingArgs on Dog {
+                    isAtLocation(x: 0)
+                    isAtLocation(y: 0)
+                }
+            ");
+        }
+
+        [Fact]
+        public void AllowsDifferentArgsWhereNoConflictIsPossible()
+        {
+            ExpectValid(@"
+                {
+                    catOrDog {
+                        ... conflictingArgs
+                    }
+                }
+
+                fragment conflictingArgs on Pet {
+                    ... on Dog {
+                    name(surname: true)
+                    }
+                    ... on Cat {
+                    name
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void EncountersConflictInFragments()
+        {
+            ExpectErrors(@"
+                {
+                    ...A
+                    ...B
+                }
+
+                fragment A on Query {
+                    x: a
+                }
+
+                fragment B on Query {
+                    x: b
+                }
+            ");
+        }
+
+        [Fact]
+        public void ReportsEachConflictOnce()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        ...A
+                        ...B
+                    }
+                    f2 {
+                        ...B
+                        ...A
+                    }
+                    f3 {
+                        ...A
+                        ...B
+                        x: c
+                    }
+                }
+
+                fragment A on Query {
+                    x: a
+                }
+
+                fragment B on Query {
+                    x: b
+                }
+            ");
+        }
+
+        [Fact]
+        public void DeepConflict()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        x: a
+                    }
+                    f1 {
+                        x: b
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void DeepConflictWithMultipleIssues()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        x: a
+                        y: c
+                    },
+                    f1 {
+                        x: b
+                        y: d
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void VeryDeepConflict()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        f2 {
+                            x: a
+                        }
+                    }
+                    f1 {
+                        f2 {
+                            x: b
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void ReportsDeepConflictToNearestCommonAncestor()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        f2 {
+                            x: a
+                        }
+                        f2 {
+                            x: b
+                        }
+                    }
+                    f1 {
+                        f2 {
+                            y
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void ReportsDeepConflictToNearestCommonAncestorInFragments()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        ...F
+                    }
+                    f1 {
+                        ...F
+                    }
+                }
+                fragment F on Query {
+                    f2 {
+                        f3 {
+                            x: a
+                        }
+                        f3 {
+                            x: b
+                        }
+                    },
+                    f2 {
+                        f3 {
+                            y
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void ReportsDeepConflictInNestedFragments()
+        {
+            ExpectErrors(@"
+                {
+                    f1 {
+                        ...F
+                    }
+                    f1 {
+                        ...I
+                    }
+                }
+
+                fragment F on Query {
+                    x: a
+                    ...G
+                }
+
+                fragment G on Query {
+                    y: c
+                }
+
+                fragment I on Query {
+                    y: d
+                    ...J
+                }
+
+                fragment J on Query {
+                    x: b
+                }
+            ");
+        }
+
+
+        [Fact]
+        public void ConflictingReturnTypesWhichPotentiallyOverlap()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ...on IntBox {
+                            scalar
+                        }
+                        ...on NonNullStringBox1 {
+                            scalar
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void CompatibleReturnShapesOnDifferentReturnTypes()
+        {
+            ExpectValid(TestSchema, @"
+                {
+                    someBox {
+                        ... on SomeBox {
+                            deepBox {
+                                unrelatedField
+                            }
+                        }
+                        ... on StringBox {
+                            deepBox {
+                                unrelatedField
+                            }
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void DisallowsDifferingReturnTypesDespiteNoOverlap()
+        {
+            ExpectErrors(TestSchema, @"
+            {
+                someBox {
+                    ... on IntBox {
+                        scalar
+                    }
+                    ... on StringBox {
+                        scalar
+                    }
+                }
+            }
+            ");
+        }
+
+        [Fact]
+        public void DisallowsDifferingReturnTypeNullabilityDespiteNoOverlap()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ... on NonNullStringBox1 {
+                            scalar
+                        }
+                        ... on StringBox {
+                            scalar
+                        }
+                    }
+                }
+            ");
+        }
+
+        [Fact]
+        public void DisallowsDifferingReturnTypeListDespiteNoOverlap()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ... on IntBox {
+                            box: listStringBox {
+                                scalar
+                            }
+                        }
+                        ... on StringBox {
+                            box: stringBox {
+                                scalar
+                            }
+                        }
+                    }
+                }");
+        }
+
+        [Fact]
+        public void DisallowsDifferingReturnTypeListDespiteNoOverlapReverse()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ... on IntBox {
+                            box: stringBox {
+                                scalar
+                            }
+                        }
+                        ... on StringBox {
+                            box: listStringBox {
+                                scalar
+                            }
+                        }
+                    }
+                }");
+        }
+
+        [Fact]
+        public void DisallowsDifferingSubfields()
+        {
+            ExpectErrors(TestSchema,
+                @"{
+                    someBox {
+                        ... on IntBox {
+                            box: stringBox {
+                                val: scalar
+                                val: unrelatedField
+                            }
+                        }
+                        ... on StringBox {
+                            box: stringBox {
+                                val: scalar
+                            }
+                        }
+                    }
+                }");
+        }
+
+        // TODO : Fix this issue
+        [Fact(Skip = "This one needs fixing!")]
+        public void DisallowsDifferingDeepReturnTypesDespiteNoOverlap()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ... on IntBox {
+                            box: stringBox {
+                                scalar
+                            }
+                        }
+                        ... on StringBox {
+                            box: intBox {
+                                scalar
+                            }
+                        }
+                    }
+                }");
+        }
+
+        [Fact]
+        public void AllowsNonConflictingOverlappingTypes()
+        {
+            ExpectValid(TestSchema, @"
+                {
+                    someBox {
+                        ... on IntBox {
+                            scalar: unrelatedField
+                        }
+                        ... on StringBox {
+                            scalar
+                        }
+                    }
+                }");
+        }
+
+        // TODO : we need to analyze this validation issue further.
+        [Fact(Skip = "This one needs to be analyzed further.")]
+        public void SameWrappedScalarReturnTypes()
+        {
+            ExpectErrors(TestSchema, @"
+                {
+                    someBox {
+                        ...on NonNullStringBox1 {
+                            scalar
+                        }
+                        ...on NonNullStringBox2 {
+                            scalar
+                        }
+                    }
+                }");
+        }
+
+        [Fact]
+        public void AllowsInlineFragmentsWithoutTypeCondition()
+        {
+            ExpectValid(TestSchema, @"
+                {
+                    a
+                    ... {
+                        a
+                    }
+                }");
+        }
+
+        [Fact]
+        public void ComparesDeepTypesIncludingList()
+        {
+            ExpectErrors(TestSchema, @"
+            {
+                connection {
+                    ...edgeID
+                    edges {
+                        node {
+                            id: name
+                        }
+                    }
+                }
+            }
+
+            fragment edgeID on Connection {
+                edges {
+                    node {
+                        id
+                    }
+                }
+            }");
+        }
+
+        [Fact]
+        public void FindsInvalidCaseEvenWithImmediatelyRecursiveFragment()
+        {
+            ExpectErrors(@"
+                {
+                    dogOrHuman {
+                        ... sameAliasesWithDifferentFieldTargets
+                    }
+                }
+
+                fragment sameAliasesWithDifferentFieldTargets on Dog {
+                    ...sameAliasesWithDifferentFieldTargets
+                    fido: name
+                    fido: nickname
+                }");
+        }
+
+        private static readonly ISchema TestSchema =
+            SchemaBuilder.New()
+                .AddDocumentFromString(@"
+                    interface SomeBox {
+                        deepBox: SomeBox
+                        unrelatedField: String
+                    }
+                    type StringBox implements SomeBox {
+                        scalar: String
+                        deepBox: StringBox
+                        unrelatedField: String
+                        listStringBox: [StringBox]
+                        stringBox: StringBox
+                        intBox: IntBox
+                    }
+                    type IntBox implements SomeBox {
+                        scalar: Int
+                        deepBox: IntBox
+                        unrelatedField: String
+                        listStringBox: [StringBox]
+                        stringBox: StringBox
+                        intBox: IntBox
+                    }
+                    interface NonNullStringBox1 {
+                        scalar: String!
+                    }
+                    type NonNullStringBox1Impl implements SomeBox & NonNullStringBox1 {
+                        scalar: String!
+                        unrelatedField: String
+                        deepBox: SomeBox
+                    }
+                    interface NonNullStringBox2 {
+                        scalar: String!
+                    }
+                    type NonNullStringBox2Impl implements SomeBox & NonNullStringBox2 {
+                        scalar: String!
+                        unrelatedField: String
+                        deepBox: SomeBox
+                    }
+                    type Connection {
+                        edges: [Edge]
+                    }
+                    type Edge {
+                        node: Node
+                    }
+                    type Node {
+                        id: ID
+                        name: String
+                    }
+                    type Query {
+                        someBox: SomeBox
+                        connection: Connection
+                        a: String
+                        d: String
+                        y: String
+                    }")
+            .AddResolver("StringBox", "deepBox", () => "")
+            .AddResolver("StringBox", "intBox", () => "")
+            .AddResolver("StringBox", "listStringBox", () => "")
+            .AddResolver("StringBox", "scalar", () => "")
+            .AddResolver("StringBox", "stringBox", () => "")
+            .AddResolver("StringBox", "unrelatedField", () => "")
+            .AddResolver("IntBox", "deepBox", () => "")
+            .AddResolver("IntBox", "intBox", () => "")
+            .AddResolver("IntBox", "listStringBox", () => "")
+            .AddResolver("IntBox", "scalar", () => "")
+            .AddResolver("IntBox", "stringBox", () => "")
+            .AddResolver("IntBox", "unrelatedField", () => "")
+            .AddResolver("NonNullStringBox1Impl", "deepBox", () => "")
+            .AddResolver("NonNullStringBox1Impl", "scalar", () => "")
+            .AddResolver("NonNullStringBox1Impl", "unrelatedField", () => "")
+            .AddResolver("NonNullStringBox2Impl", "deepBox", () => "")
+            .AddResolver("NonNullStringBox2Impl", "scalar", () => "")
+            .AddResolver("NonNullStringBox2Impl", "unrelatedField", () => "")
+            .AddResolver("Connection", "edges", () => "")
+            .AddResolver("Edge", "node", () => "")
+            .AddResolver("Node", "id", () => "")
+            .AddResolver("Node", "name", () => "")
+            .AddResolver("Query", "connection", () => "")
+            .AddResolver("Query", "someBox", () => "")
+            .AddResolver("Query", "a", () => "")
+            .AddResolver("Query", "d", () => "")
+            .AddResolver("Query", "y", () => "")
+            .AddType(new AnyType())
+            .Create();
     }
 }
diff --git a/src/HotChocolate/Core/test/Validation.Tests/FragmentSpreadsMustNotFormCyclesRuleTests.cs b/src/HotChocolate/Core/test/Validation.Tests/FragmentSpreadsMustNotFormCyclesRuleTests.cs
index c94823f1c52..b09f30a005d 100644
--- a/src/HotChocolate/Core/test/Validation.Tests/FragmentSpreadsMustNotFormCyclesRuleTests.cs
+++ b/src/HotChocolate/Core/test/Validation.Tests/FragmentSpreadsMustNotFormCyclesRuleTests.cs
@@ -355,5 +355,57 @@ public void NoSpreadingItselfDeeplyAndImmediately()
                 fragment fragC on Dog { ...fragA, ...fragB }
             ");
         }
+
+        [Fact]
+        public void DoesNotInfiniteLoopOnRecursiveFragment()
+        {
+            ExpectErrors(@"
+                {
+                    dogOrHuman {
+                        ... fragA
+                    }
+                }
+
+                fragment fragA on Human {
+                    name
+                    ... fragA
+                }");
+        }
+
+        [Fact]
+        public void DoesNotInfiniteLoopOnImmediatelyRecursiveFragment()
+        {
+            ExpectErrors(@"
+                {
+                    dogOrHuman {
+                        ... fragA
+                    }
+                }
+
+                fragment fragA on Human {
+                    name
+                    relatives {
+                        name
+                        ... fragA
+                    }
+                }");
+        }
+
+        [Fact]
+        public void DoesNotInfiniteLoopOnTransitivelyRecursiveFragment()
+        {
+            ExpectErrors(@"
+                {
+                    dogOrHuman {
+                        ... fragA
+                        ... fragB
+                        ... fragC
+                    }
+                }
+
+                fragment fragA on Human { name, ...fragB }
+                fragment fragB on Human { name, ...fragC }
+                fragment fragC on Human { name, ...fragA }");
+        }
     }
 }
diff --git a/src/HotChocolate/Core/test/Validation.Tests/Models/Query.cs b/src/HotChocolate/Core/test/Validation.Tests/Models/Query.cs
index ace78ce5dcc..1033ea04562 100644
--- a/src/HotChocolate/Core/test/Validation.Tests/Models/Query.cs
+++ b/src/HotChocolate/Core/test/Validation.Tests/Models/Query.cs
@@ -2,6 +2,24 @@
 {
     public class Query
     {
+        public string A { get; set; }
+
+        public string B { get; set; }
+
+        public string C { get; set; }
+        
+        public string D { get; set; }
+
+        public string Y { get; set; }
+
+        public Query F1 { get; set; }
+
+        public Query F2 { get; set; }
+
+        public Query F3 { get; set; }
+
+        public Query GetField() => null;
+
         public Dog GetDog()
         {
             return null;
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.AliasMaskingDirectFieldAccess.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.AliasMaskingDirectFieldAccess.snap
new file mode 100644
index 00000000000..7c4ba94f481
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.AliasMaskingDirectFieldAccess.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      },
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "nickname",
+      "fieldB": "name",
+      "typeA": "String",
+      "typeB": "String!",
+      "responseNameA": "name",
+      "responseNameB": "name",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ComparesDeepTypesIncludingList.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ComparesDeepTypesIncludingList.snap
new file mode 100644
index 00000000000..b713b2d0e75
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ComparesDeepTypesIncludingList.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 16,
+        "Column": 25
+      },
+      {
+        "Line": 7,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Node",
+      "declaringTypeB": "Node",
+      "fieldA": "id",
+      "fieldB": "name",
+      "typeA": "ID",
+      "typeB": "String",
+      "responseNameA": "id",
+      "responseNameB": "id",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgNames.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgNames.snap
new file mode 100644
index 00000000000..70bf164c694
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgNames.snap
@@ -0,0 +1,46 @@
+[
+  {
+    "Message": "The field `isAtLocation` does not exist on the type `Dog`.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "catOrDog"
+    },
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "type": "Dog",
+      "field": "isAtLocation",
+      "responseName": "isAtLocation",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "The field `isAtLocation` does not exist on the type `Dog`.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "catOrDog"
+    },
+    "Locations": [
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "type": "Dog",
+      "field": "isAtLocation",
+      "responseName": "isAtLocation",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgValues.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgValues.snap
new file mode 100644
index 00000000000..2503a0d7a5c
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingArgValues.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      },
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "doesKnowCommand",
+      "fieldB": "doesKnowCommand",
+      "typeA": "Boolean!",
+      "typeB": "Boolean!",
+      "responseNameA": "doesKnowCommand",
+      "responseNameB": "doesKnowCommand",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingReturnTypesWhichPotentiallyOverlap.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingReturnTypesWhichPotentiallyOverlap.snap
new file mode 100644
index 00000000000..02ac4a0c980
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ConflictingReturnTypesWhichPotentiallyOverlap.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 8,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "IntBox",
+      "declaringTypeB": "NonNullStringBox1",
+      "fieldA": "scalar",
+      "fieldB": "scalar",
+      "typeA": "Int",
+      "typeB": "String!",
+      "responseNameA": "scalar",
+      "responseNameB": "scalar",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflict.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflict.snap
new file mode 100644
index 00000000000..9fc1802a044
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflict.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 4,
+        "Column": 25
+      },
+      {
+        "Line": 7,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflictWithMultipleIssues.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflictWithMultipleIssues.snap
new file mode 100644
index 00000000000..d98f7f1a7b4
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DeepConflictWithMultipleIssues.snap
@@ -0,0 +1,56 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 4,
+        "Column": 25
+      },
+      {
+        "Line": 8,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 25
+      },
+      {
+        "Line": 9,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "c",
+      "fieldB": "d",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "y",
+      "responseNameB": "y",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondAddsAnArgument.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondAddsAnArgument.snap
new file mode 100644
index 00000000000..2503a0d7a5c
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondAddsAnArgument.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      },
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "doesKnowCommand",
+      "fieldB": "doesKnowCommand",
+      "typeA": "Boolean!",
+      "typeB": "Boolean!",
+      "responseNameA": "doesKnowCommand",
+      "responseNameB": "doesKnowCommand",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondMissingAnArgument.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondMissingAnArgument.snap
new file mode 100644
index 00000000000..2503a0d7a5c
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DifferentArgsSecondMissingAnArgument.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      },
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "doesKnowCommand",
+      "fieldB": "doesKnowCommand",
+      "typeA": "Boolean!",
+      "typeB": "Boolean!",
+      "responseNameA": "doesKnowCommand",
+      "responseNameB": "doesKnowCommand",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlap.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlap.snap
new file mode 100644
index 00000000000..1d1406a240a
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlap.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 10,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "IntBox",
+      "declaringTypeB": "StringBox",
+      "fieldA": "listStringBox",
+      "fieldB": "stringBox",
+      "typeA": "[StringBox]",
+      "typeB": "StringBox",
+      "responseNameA": "box",
+      "responseNameB": "box",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlapReverse.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlapReverse.snap
new file mode 100644
index 00000000000..be9d20d22a4
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeListDespiteNoOverlapReverse.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 10,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "IntBox",
+      "declaringTypeB": "StringBox",
+      "fieldA": "stringBox",
+      "fieldB": "listStringBox",
+      "typeA": "StringBox",
+      "typeB": "[StringBox]",
+      "responseNameA": "box",
+      "responseNameB": "box",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeNullabilityDespiteNoOverlap.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeNullabilityDespiteNoOverlap.snap
new file mode 100644
index 00000000000..76a8849ade0
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypeNullabilityDespiteNoOverlap.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 8,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "NonNullStringBox1",
+      "declaringTypeB": "StringBox",
+      "fieldA": "scalar",
+      "fieldB": "scalar",
+      "typeA": "String!",
+      "typeB": "String",
+      "responseNameA": "scalar",
+      "responseNameB": "scalar",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypesDespiteNoOverlap.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypesDespiteNoOverlap.snap
new file mode 100644
index 00000000000..2269eabca2c
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingReturnTypesDespiteNoOverlap.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 25
+      },
+      {
+        "Line": 8,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "IntBox",
+      "declaringTypeB": "StringBox",
+      "fieldA": "scalar",
+      "fieldB": "scalar",
+      "typeA": "Int",
+      "typeB": "String",
+      "responseNameA": "scalar",
+      "responseNameB": "scalar",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingSubfields.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingSubfields.snap
new file mode 100644
index 00000000000..2bb96b3f2bc
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DisallowsDifferingSubfields.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 33
+      },
+      {
+        "Line": 6,
+        "Column": 33
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "StringBox",
+      "declaringTypeB": "StringBox",
+      "fieldA": "scalar",
+      "fieldB": "unrelatedField",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "val",
+      "responseNameB": "val",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap
new file mode 100644
index 00000000000..cd01c3bebff
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap
@@ -0,0 +1,20 @@
+[
+  {
+    "Message": "The field `` does not exist on the type `Query`.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 3,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "type": "Query",
+      "field": "",
+      "responseName": "",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap
new file mode 100644
index 00000000000..cd01c3bebff
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap
@@ -0,0 +1,20 @@
+[
+  {
+    "Message": "The field `` does not exist on the type `Query`.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 3,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "type": "Query",
+      "field": "",
+      "responseName": "",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap
new file mode 100644
index 00000000000..cd01c3bebff
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap
@@ -0,0 +1,20 @@
+[
+  {
+    "Message": "The field `` does not exist on the type `Query`.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 3,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "type": "Query",
+      "field": "",
+      "responseName": "",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.EncountersConflictInFragments.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.EncountersConflictInFragments.snap
new file mode 100644
index 00000000000..6c249ae4b91
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.EncountersConflictInFragments.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 8,
+        "Column": 21
+      },
+      {
+        "Line": 12,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.FindsInvalidCaseEvenWithImmediatelyRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.FindsInvalidCaseEvenWithImmediatelyRecursiveFragment.snap
new file mode 100644
index 00000000000..bc37acb9e9d
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.FindsInvalidCaseEvenWithImmediatelyRecursiveFragment.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 10,
+        "Column": 21
+      },
+      {
+        "Line": 11,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "name",
+      "fieldB": "nickname",
+      "typeA": "String!",
+      "typeB": "String",
+      "responseNameA": "fido",
+      "responseNameB": "fido",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictInNestedFragments.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictInNestedFragments.snap
new file mode 100644
index 00000000000..680e37ea963
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictInNestedFragments.snap
@@ -0,0 +1,56 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 12,
+        "Column": 21
+      },
+      {
+        "Line": 26,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 17,
+        "Column": 21
+      },
+      {
+        "Line": 21,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "c",
+      "fieldB": "d",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "y",
+      "responseNameB": "y",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestor.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestor.snap
new file mode 100644
index 00000000000..94070231bf1
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestor.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 8,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestorInFragments.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestorInFragments.snap
new file mode 100644
index 00000000000..95bbdd5867d
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsDeepConflictToNearestCommonAncestorInFragments.snap
@@ -0,0 +1,56 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 13,
+        "Column": 29
+      },
+      {
+        "Line": 16,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 16,
+        "Column": 29
+      },
+      {
+        "Line": 13,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "b",
+      "fieldB": "a",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsEachConflictOnce.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsEachConflictOnce.snap
new file mode 100644
index 00000000000..5e0f3917025
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.ReportsEachConflictOnce.snap
@@ -0,0 +1,110 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 19,
+        "Column": 21
+      },
+      {
+        "Line": 23,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 23,
+        "Column": 21
+      },
+      {
+        "Line": 19,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "b",
+      "fieldB": "a",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 19,
+        "Column": 21
+      },
+      {
+        "Line": 14,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "c",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 23,
+        "Column": 21
+      },
+      {
+        "Line": 14,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "b",
+      "fieldB": "c",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesAllowedOnNonOverlappingFields.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesAllowedOnNonOverlappingFields.snap
new file mode 100644
index 00000000000..803318341cb
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesAllowedOnNonOverlappingFields.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 10,
+        "Column": 25
+      },
+      {
+        "Line": 13,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Cat",
+      "fieldA": "name",
+      "fieldB": "nickname",
+      "typeA": "String!",
+      "typeB": "String",
+      "responseNameA": "name",
+      "responseNameB": "name",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesWithDifferentFieldTargets.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesWithDifferentFieldTargets.snap
new file mode 100644
index 00000000000..45f6b4a4ad7
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.SameAliasesWithDifferentFieldTargets.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 9,
+        "Column": 21
+      },
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Dog",
+      "declaringTypeB": "Dog",
+      "fieldA": "name",
+      "fieldB": "nickname",
+      "typeA": "String!",
+      "typeB": "String",
+      "responseNameA": "fido",
+      "responseNameB": "fido",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.VeryDeepConflict.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.VeryDeepConflict.snap
new file mode 100644
index 00000000000..83df27fbf1f
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FieldSelectionMergingRuleTests.VeryDeepConflict.snap
@@ -0,0 +1,29 @@
+[
+  {
+    "Message": "Encountered fields for the same object that cannot be merged.",
+    "Code": null,
+    "Path": null,
+    "Locations": [
+      {
+        "Line": 5,
+        "Column": 29
+      },
+      {
+        "Line": 10,
+        "Column": 29
+      }
+    ],
+    "Extensions": {
+      "declaringTypeA": "Query",
+      "declaringTypeB": "Query",
+      "fieldA": "a",
+      "fieldB": "b",
+      "typeA": "String",
+      "typeB": "String",
+      "responseNameA": "x",
+      "responseNameB": "x",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Field-Selection-Merging"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap
new file mode 100644
index 00000000000..44bf506e383
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnImmediatelyRecursiveFragment.snap
@@ -0,0 +1,26 @@
+[
+  {
+    "Message": "The graph of fragment spreads must not form any cycles including spreading itself. Otherwise an operation could infinitely spread or infinitely execute on cycles in the underlying data.",
+    "Code": null,
+    "Path": {
+      "Parent": {
+        "Parent": null,
+        "Depth": 0,
+        "Name": "dogOrHuman"
+      },
+      "Depth": 1,
+      "Name": "relatives"
+    },
+    "Locations": [
+      {
+        "Line": 12,
+        "Column": 25
+      }
+    ],
+    "Extensions": {
+      "fragment": "fragA",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Fragment-spreads-must-not-form-cycles"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap
new file mode 100644
index 00000000000..3a5a77ba1de
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnRecursiveFragment.snap
@@ -0,0 +1,22 @@
+[
+  {
+    "Message": "The graph of fragment spreads must not form any cycles including spreading itself. Otherwise an operation could infinitely spread or infinitely execute on cycles in the underlying data.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "dogOrHuman"
+    },
+    "Locations": [
+      {
+        "Line": 10,
+        "Column": 21
+      }
+    ],
+    "Extensions": {
+      "fragment": "fragA",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Fragment-spreads-must-not-form-cycles"
+    },
+    "Exception": null
+  }
+]
diff --git a/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap
new file mode 100644
index 00000000000..9077997151e
--- /dev/null
+++ b/src/HotChocolate/Core/test/Validation.Tests/__snapshots__/FragmentSpreadsMustNotFormCyclesRuleTests.DoesNotInfiniteLoopOnTransitivelyRecursiveFragment.snap
@@ -0,0 +1,62 @@
+[
+  {
+    "Message": "The graph of fragment spreads must not form any cycles including spreading itself. Otherwise an operation could infinitely spread or infinitely execute on cycles in the underlying data.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "dogOrHuman"
+    },
+    "Locations": [
+      {
+        "Line": 12,
+        "Column": 49
+      }
+    ],
+    "Extensions": {
+      "fragment": "fragA",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Fragment-spreads-must-not-form-cycles"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "The graph of fragment spreads must not form any cycles including spreading itself. Otherwise an operation could infinitely spread or infinitely execute on cycles in the underlying data.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "dogOrHuman"
+    },
+    "Locations": [
+      {
+        "Line": 10,
+        "Column": 49
+      }
+    ],
+    "Extensions": {
+      "fragment": "fragB",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Fragment-spreads-must-not-form-cycles"
+    },
+    "Exception": null
+  },
+  {
+    "Message": "The graph of fragment spreads must not form any cycles including spreading itself. Otherwise an operation could infinitely spread or infinitely execute on cycles in the underlying data.",
+    "Code": null,
+    "Path": {
+      "Parent": null,
+      "Depth": 0,
+      "Name": "dogOrHuman"
+    },
+    "Locations": [
+      {
+        "Line": 11,
+        "Column": 49
+      }
+    ],
+    "Extensions": {
+      "fragment": "fragC",
+      "specifiedBy": "http://spec.graphql.org/June2018/#sec-Fragment-spreads-must-not-form-cycles"
+    },
+    "Exception": null
+  }
+]