diff --git a/app.rb b/app.rb
index bc8e508..778d498 100644
--- a/app.rb
+++ b/app.rb
@@ -8,6 +8,7 @@
 # Require base
 require 'sinatra/base'
 
+require 'app/errors'
 require 'app/models'
 require 'app/routes'
 
diff --git a/app/errors.rb b/app/errors.rb
new file mode 100644
index 0000000..63a077f
--- /dev/null
+++ b/app/errors.rb
@@ -0,0 +1,8 @@
+module Lorry
+  module Errors
+
+    class ComposeValidationWarning < Kwalify::ValidationError
+    end
+
+  end
+end
diff --git a/app/models/validation.rb b/app/models/validation.rb
index 83bac58..451e9f5 100644
--- a/app/models/validation.rb
+++ b/app/models/validation.rb
@@ -4,7 +4,9 @@ class Validation
 
       def initialize(document)
         validator = ComposeValidator.new
-        validator.services = YAML.load(document).keys
+        if yaml = YAML.load(document)
+          validator.services = yaml.keys if yaml.respond_to?(:keys)
+        end
         @parser = Kwalify::Yaml::Parser.new(validator)
         @parser.parse(document) if document
       rescue Kwalify::SyntaxError => e
@@ -12,7 +14,11 @@ def initialize(document)
       end
 
       def errors
-        @parser.errors unless Array(@parser.errors).empty?
+        @parser.errors.map { |err| err if err.instance_of? Kwalify::ValidationError }.compact
+      end
+
+      def warnings
+        @parser.errors.map { |err| err if err.instance_of? Lorry::Errors::ComposeValidationWarning }.compact
       end
     end
   end
diff --git a/app/routes/validation.rb b/app/routes/validation.rb
index aa97ee5..8fea129 100644
--- a/app/routes/validation.rb
+++ b/app/routes/validation.rb
@@ -17,7 +17,12 @@ class Validation < Base
         post do
           @document = @payload[:document]
           @validation = Lorry::Models::Validation.new(@document)
-          json(lines: document_lines, status: validation_status, errors: validation_errors)
+          json(
+            lines: document_lines,
+            status: validation_status,
+            errors: validation_errors,
+            warnings: validation_warnings
+          )
         end
       end
 
@@ -34,6 +39,12 @@ def validation_errors
         end
       end
 
+      def validation_warnings
+        Array(@validation.warnings).map do |w|
+          { warning: { message: w.message, line: w.linenum, column: w.column } }
+        end
+      end
+
       def validation_status
         @validation.errors ? 'invalid' : 'valid'
       end
diff --git a/spec/models/validation_spec.rb b/spec/models/validation_spec.rb
new file mode 100644
index 0000000..c8dbf5f
--- /dev/null
+++ b/spec/models/validation_spec.rb
@@ -0,0 +1,54 @@
+require 'spec_helper'
+
+describe Validation do
+  let(:parser_with_errors) do
+    double('parser',
+           parse: true,
+           errors: [Kwalify::ValidationError.new('error'),
+                    Lorry::Errors::ComposeValidationWarning.new('warning')])
+  end
+  let(:parser_without_errors) { double('parser', errors: [], warnings: []) }
+  let(:validator) { double('validator') }
+
+  before do
+    allow(ComposeValidator).to receive(:new).and_return(validator)
+    allow(validator).to receive(:services=).and_return(true)
+    allow(YAML).to receive(:load).and_return(double(keys:[]))
+  end
+
+  describe '#errors' do
+    context('when the document has errors') do
+      before do
+        allow(Kwalify::Yaml::Parser).to receive(:new).and_return(parser_with_errors)
+      end
+
+      subject { Lorry::Models::Validation.new(nil) }
+
+      it('returns an array') do
+        expect(subject.errors).to be_an(Array)
+      end
+
+      it('returns an array with only Kwalify::ValidationError instances') do
+        expect(subject.errors).to all(be_an_instance_of Kwalify::ValidationError)
+      end
+    end
+  end
+
+  describe '#warnings' do
+    context('when the document has warnings') do
+      before do
+        allow(Kwalify::Yaml::Parser).to receive(:new).and_return(parser_with_errors)
+      end
+
+      subject { Lorry::Models::Validation.new(nil) }
+
+      it('returns an array') do
+        expect(subject.warnings).to be_an(Array)
+      end
+
+      it('returns an array with only Kwalify::ValidationError instances') do
+        expect(subject.warnings).to all(be_an_instance_of Lorry::Errors::ComposeValidationWarning)
+      end
+    end
+  end
+end
diff --git a/spec/routes/validations_spec.rb b/spec/routes/validations_spec.rb
new file mode 100644
index 0000000..13667c6
--- /dev/null
+++ b/spec/routes/validations_spec.rb
@@ -0,0 +1,70 @@
+require 'spec_helper'
+
+describe Lorry::Routes::Validation do
+
+  describe 'OPTIONS /validation' do
+    it 'returns a response with status code 200' do
+      response = options '/validation'
+      expect(response.status).to be 200
+    end
+  end
+
+  describe 'POST validations' do
+
+    let(:request_body) { { document: "" }.to_json }
+
+    it 'returns a response with status code 200' do
+      response = post '/validation', request_body
+      expect(response.status).to eq 200
+    end
+
+    it 'returns a JSON object with an array of lines' do
+      response = post '/validation', request_body
+      expect(JSON.parse(response.body)['lines']).to eq []
+    end
+
+    it 'returns a JSON object with a status indicator' do
+      response = post '/validation', request_body
+      expect(JSON.parse(response.body)['status']).to eq 'invalid'
+    end
+
+    it 'returns a JSON object with an array of errors' do
+      response = post '/validation', request_body
+      expect(JSON.parse(response.body)['errors']).to eq []
+    end
+
+    it 'returns a JSON object with an array of warnings' do
+      response = post '/validation', request_body
+      expect(JSON.parse(response.body)['warnings']).to eq []
+    end
+
+    context('when the validation returns errors') do
+      let(:request_body) { { document: "foo" }.to_json }
+
+      it 'the errors array contains an error object with message, line, and column attributes' do
+        response = post '/validation', request_body
+        errors = JSON.parse(response.body)['errors']
+        expect(errors.first['error'].keys).to match_array(%w(message line column))
+      end
+    end
+
+    context('when the validation returns warnings') do
+      let(:warnings) do
+        [Lorry::Errors::ComposeValidationWarning.new('warning')]
+      end
+      let(:validation) { double('validation', warnings: warnings, errors: nil) }
+      let(:request_body) { { document: "" }.to_json }
+
+      before do
+        allow(Lorry::Models::Validation).to receive(:new).and_return(validation)
+      end
+
+      it 'the warnings array contains a warning object with message, line, and column attributes' do
+        response = post '/validation', request_body
+        errors = JSON.parse(response.body)['warnings']
+        expect(errors.first['warning'].keys).to match_array(%w(message line column))
+      end
+    end
+  end
+
+end