diff --git a/api/logic/minecraft/ComponentList.cpp b/api/logic/minecraft/ComponentList.cpp
index e5c373a458..c946d4b4a7 100644
--- a/api/logic/minecraft/ComponentList.cpp
+++ b/api/logic/minecraft/ComponentList.cpp
@@ -981,7 +981,7 @@ bool ComponentList::removeComponent_internal(ComponentPtr patch)
     // FIXME: we need a generic way of removing local resources, not just jar mods...
     auto preRemoveJarMod = [&](LibraryPtr jarMod) -> bool
     {
-        if (!jarMod->isLocal())
+        if (!jarMod->isInstanceLocal())
         {
             return true;
         }
diff --git a/api/logic/minecraft/GradleSpecifier.h b/api/logic/minecraft/GradleSpecifier.h
index 959325c6d4..e963c44297 100644
--- a/api/logic/minecraft/GradleSpecifier.h
+++ b/api/logic/minecraft/GradleSpecifier.h
@@ -117,7 +117,7 @@ struct GradleSpecifier
     }
     bool matchName(const GradleSpecifier & other) const
     {
-        return other.artifactId() == artifactId() && other.groupId() == groupId();
+        return other.artifactId() == artifactId() && other.groupId() == groupId() && other.classifier() == classifier();
     }
     bool operator==(const GradleSpecifier & other) const
     {
diff --git a/api/logic/minecraft/Library.cpp b/api/logic/minecraft/Library.cpp
index a56e81104c..acff662e04 100644
--- a/api/logic/minecraft/Library.cpp
+++ b/api/logic/minecraft/Library.cpp
@@ -11,7 +11,7 @@
 void Library::getApplicableFiles(OpSys system, QStringList& jar, QStringList& native, QStringList& native32,
                                  QStringList& native64, const QString &overridePath) const
 {
-    bool local = isLocal();
+    bool local = isInstanceLocal();
     auto actualPath = [&](QString relPath)
     {
         QFileInfo out(FS::PathCombine(storagePrefix(), relPath));
@@ -39,7 +39,7 @@ void Library::getApplicableFiles(OpSys system, QStringList& jar, QStringList& na
             native += actualPath(raw_storage);
         }
     }
-    else
+    else if (!presenceOnly)
     {
         jar += actualPath(raw_storage);
     }
@@ -54,9 +54,10 @@ QList< std::shared_ptr< NetAction > > Library::getDownloads(
 {
     QList<NetActionPtr> out;
     bool stale = isAlwaysStale();
-    bool local = isLocal();
+    bool instanceLocal = isInstanceLocal();
+    bool launcherLocal = isLocalBuilt();
 
-    auto check_local_file = [&](QString storage)
+    auto check_instance_local_file = [&](QString storage)
     {
         QFileInfo fileinfo(storage);
         QString fileName = fileinfo.fileName();
@@ -70,11 +71,26 @@ QList< std::shared_ptr< NetAction > > Library::getDownloads(
         return true;
     };
 
+    auto check_launcher_local_file = [&](QString storage)
+    {
+        QFileInfo localFileInfo("libraries/" + storage);
+        if(!localFileInfo.exists())
+        {
+            failedLocalFiles.append(localFileInfo.filePath());
+            return false;
+        }
+        return true;
+    };
+
     auto add_download = [&](QString storage, QString url, QString sha1)
     {
-        if(local)
+        if(instanceLocal)
+        {
+            return check_instance_local_file(storage);
+        }
+        else if(launcherLocal)
         {
-            return check_local_file(storage);
+            return check_launcher_local_file(storage);
         }
         auto entry = cache->resolveEntry("libraries", storage);
         if(stale)
@@ -233,11 +249,16 @@ bool Library::isActive() const
     return result;
 }
 
-bool Library::isLocal() const
+bool Library::isInstanceLocal() const
 {
     return m_hint == "local";
 }
 
+bool Library::isLocalBuilt() const
+{
+    return localBuild;
+}
+
 bool Library::isAlwaysStale() const
 {
     return m_hint == "always-stale";
diff --git a/api/logic/minecraft/Library.h b/api/logic/minecraft/Library.h
index 014f674543..2f20229161 100644
--- a/api/logic/minecraft/Library.h
+++ b/api/logic/minecraft/Library.h
@@ -49,6 +49,8 @@ class MULTIMC_LOGIC_EXPORT Library
         newlib->m_storagePrefix = base->m_storagePrefix;
         newlib->m_mojangDownloads = base->m_mojangDownloads;
         newlib->m_filename = base->m_filename;
+        newlib->presenceOnly = base->presenceOnly;
+        newlib->localBuild = base->localBuild;
         return newlib;
     }
 
@@ -146,7 +148,15 @@ class MULTIMC_LOGIC_EXPORT Library
     bool isActive() const;
 
     /// Returns true if the library is contained in an instance and false if it is shared
-    bool isLocal() const;
+    bool isInstanceLocal() const;
+
+    /// Returns true if the library cannot be downloaded (was built locally somehow)
+    bool isLocalBuilt() const;
+
+    bool isLocal() const
+    {
+        return isInstanceLocal() || isLocalBuilt();
+    }
 
     /// Returns true if the library is to always be checked for updates
     bool isAlwaysStale() const;
@@ -212,6 +222,12 @@ class MULTIMC_LOGIC_EXPORT Library
     /// true if the library had a rules section (even empty)
     bool applyRules = false;
 
+    // MultiMC-specific: the artifact must be present, but is not part of the classpath
+    bool presenceOnly = false;
+
+    // MultiMC-specific: the artifact must be present, but cannot be downloaded, because it was created by some other mechanism
+    bool localBuild = false;
+
     /// rules associated with the library
     QList<std::shared_ptr<Rule>> m_rules;
 
diff --git a/api/logic/minecraft/MojangDownloadInfo.h b/api/logic/minecraft/MojangDownloadInfo.h
index 88f87287d9..1fa1c5bd01 100644
--- a/api/logic/minecraft/MojangDownloadInfo.h
+++ b/api/logic/minecraft/MojangDownloadInfo.h
@@ -36,7 +36,7 @@ struct MojangLibraryDownloadInfo
         {
             return artifact.get();
         }
-        
+
         return classifiers[classifier].get();
     }
 
diff --git a/api/logic/minecraft/MojangVersionFormat.cpp b/api/logic/minecraft/MojangVersionFormat.cpp
index 33d3c54cb2..a8fbea656b 100644
--- a/api/logic/minecraft/MojangVersionFormat.cpp
+++ b/api/logic/minecraft/MojangVersionFormat.cpp
@@ -31,7 +31,7 @@ static void readDownloadInfo(MojangDownloadInfo::Ptr out, const QJsonObject &obj
     readString(obj, "path", out->path);
     // required!
     out->sha1 = requireString(obj, "sha1");
-    out->url = requireString(obj, "url");
+    out->url = ensureString(obj, "url", QString());
     out->size = requireInteger(obj, "size");
 }
 
diff --git a/api/logic/minecraft/OneSixVersionFormat.cpp b/api/logic/minecraft/OneSixVersionFormat.cpp
index 6f3b926ba1..63bcf002ea 100644
--- a/api/logic/minecraft/OneSixVersionFormat.cpp
+++ b/api/logic/minecraft/OneSixVersionFormat.cpp
@@ -21,6 +21,14 @@ LibraryPtr OneSixVersionFormat::libraryFromJson(const QJsonObject &libObj, const
     readString(libObj, "MMC-absoluteUrl", out->m_absoluteURL);
     readString(libObj, "MMC-filename", out->m_filename);
     readString(libObj, "MMC-displayname", out->m_displayname);
+    if (libObj.contains("presenceOnly"))
+    {
+        out->presenceOnly = requireBoolean(libObj, "presenceOnly");
+    }
+    if (libObj.contains("localBuild"))
+    {
+        out->localBuild = requireBoolean(libObj, "localBuild");
+    }
     return out;
 }
 
@@ -35,6 +43,10 @@ QJsonObject OneSixVersionFormat::libraryToJson(Library *library)
         libRoot.insert("MMC-filename", library->m_filename);
     if (library->m_displayname.size())
         libRoot.insert("MMC-displayname", library->m_displayname);
+    if (library->presenceOnly)
+        libRoot.insert("presenceOnly", true);
+    if (library->localBuild)
+        libRoot.insert("localBuild", true);
     return libRoot;
 }