diff --git a/CMakeLists.txt b/CMakeLists.txt
index c8f84b28..ac497f46 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -427,6 +427,9 @@ SET(MULTIMC_SOURCES
 	# RW lock protected map
 	logic/RWStorage.h
 
+	# A variable that has an implicit default value and keeps track of changes
+	logic/DefaultVariable.h
+
 	# network stuffs
 	logic/net/NetAction.h
 	logic/net/MD5EtagDownload.h
@@ -493,6 +496,7 @@ SET(MULTIMC_SOURCES
 	logic/OneSixInstance_p.h
 
 	# OneSix version json infrastructure
+	logic/minecraft/GradleSpecifier.h
 	logic/minecraft/InstanceVersion.cpp
 	logic/minecraft/InstanceVersion.h
 	logic/minecraft/JarMod.cpp
diff --git a/logic/DefaultVariable.h b/logic/DefaultVariable.h
new file mode 100644
index 00000000..38d7ecc2
--- /dev/null
+++ b/logic/DefaultVariable.h
@@ -0,0 +1,35 @@
+#pragma once
+
+template <typename T>
+class DefaultVariable
+{
+public:
+	DefaultVariable(const T & value)
+	{
+		defaultValue = value;
+	}
+	DefaultVariable<T> & operator =(const T & value)
+	{
+		currentValue = value;
+		is_default = currentValue == defaultValue;
+		is_explicit = true;
+		return *this;
+	}
+	operator const T &() const
+	{
+		return is_default ? defaultValue : currentValue;
+	}
+	bool isDefault() const
+	{
+		return is_default;
+	}
+	bool isExplicit() const
+	{
+		return is_explicit;
+	}
+private:
+	T currentValue;
+	T defaultValue;
+	bool is_default = true;
+	bool is_explicit = false;
+};
diff --git a/logic/InstanceList.cpp b/logic/InstanceList.cpp
index 8a68c334..650f5c80 100644
--- a/logic/InstanceList.cpp
+++ b/logic/InstanceList.cpp
@@ -331,7 +331,29 @@ QSet<FTBRecord> InstanceList::discoverFTBInstances()
 						continue;
 					record.name = attrs.value("name").toString();
 					record.logo = attrs.value("logo").toString();
-					record.mcVersion = attrs.value("mcVersion").toString();
+					auto customVersions = attrs.value("customMCVersions");
+					if(!customVersions.isNull())
+					{
+						QMap<QString, QString> versionMatcher;
+						QString customVersionsStr = customVersions.toString();
+						QStringList list = customVersionsStr.split(';');
+						for(auto item: list)
+						{
+							auto segment = item.split('^');
+							if(segment.size() != 2)
+							{
+								QLOG_ERROR() << "FTB: Segment of size < 2 in " << customVersionsStr;
+								continue;
+							}
+							versionMatcher[segment[0]] = segment[1];
+						}
+						auto actualVersion = attrs.value("version").toString();
+						record.mcVersion = versionMatcher[actualVersion];
+					}
+					else
+					{
+						record.mcVersion = attrs.value("mcVersion").toString();
+					}
 					record.description = attrs.value("description").toString();
 					records.insert(record);
 				}
diff --git a/logic/minecraft/GradleSpecifier.h b/logic/minecraft/GradleSpecifier.h
new file mode 100644
index 00000000..3ee40b86
--- /dev/null
+++ b/logic/minecraft/GradleSpecifier.h
@@ -0,0 +1,83 @@
+#pragma once
+
+#include <QString>
+#include <QStringList>
+#include "logic/DefaultVariable.h"
+
+struct GradleSpecifier
+{
+	GradleSpecifier()
+	{
+		m_valid = false;
+	}
+	GradleSpecifier(QString value)
+	{
+		operator=(value);
+	}
+	GradleSpecifier & operator =(const QString & value)
+	{
+		/*
+		org.gradle.test.classifiers : service : 1.0 : jdk15 @ jar
+		DEBUG   0 "org.gradle.test.classifiers:service:1.0:jdk15@jar" 
+		DEBUG   1 "org.gradle.test.classifiers" 
+		DEBUG   2 "service" 
+		DEBUG   3 "1.0" 
+		DEBUG   4 ":jdk15" 
+		DEBUG   5 "jdk15" 
+		DEBUG   6 "@jar" 
+		DEBUG   7 "jar"
+		*/
+		QRegExp matcher("([^:@]+):([^:@]+):([^:@]+)" "(:([^:@]+))?" "(@([^:@]+))?");
+		m_valid = matcher.exactMatch(value);
+		auto elements = matcher.capturedTexts();
+		groupId = elements[1];
+		artifactId = elements[2];
+		version = elements[3];
+		classifier = elements[5];
+		if(!elements[7].isEmpty())
+		{
+			extension = elements[7];
+		}
+		return *this;
+	}
+	operator QString() const
+	{
+		if(!m_valid)
+			return "INVALID";
+		QString retval = groupId + ":" + artifactId + ":" + version;
+		if(!classifier.isEmpty())
+		{
+			retval += ":" + classifier;
+		}
+		if(extension.isExplicit())
+		{
+			retval += "@" + extension;
+		}
+		return retval;
+	}
+	QString toPath() const
+	{
+		if(!m_valid)
+			return "INVALID";
+		QString path = groupId;
+		path.replace('.', '/');
+		path += '/' + artifactId + '/' + version + '/' + artifactId + '-' + version;
+		if(!classifier.isEmpty())
+		{
+			path += "-" + classifier;
+		}
+		path += "." + extension;
+		return path;
+	}
+	bool valid()
+	{
+		return m_valid;
+	}
+private:
+	QString groupId;
+	QString artifactId;
+	QString version;
+	QString classifier;
+	DefaultVariable<QString> extension = DefaultVariable<QString>("jar");
+	bool m_valid = false;
+};
diff --git a/logic/minecraft/OneSixLibrary.cpp b/logic/minecraft/OneSixLibrary.cpp
index 7f69d9f8..f9a274bd 100644
--- a/logic/minecraft/OneSixLibrary.cpp
+++ b/logic/minecraft/OneSixLibrary.cpp
@@ -65,7 +65,10 @@ void OneSixLibrary::finalize()
 	m_decentname = parts[1];
 	m_decentversion = minVersion = parts[2];
 	m_storage_path = relative;
-	m_download_url = m_base_url + relative;
+	if(m_base_url.isEmpty())
+		m_download_url = QString("https://" + URLConstants::LIBRARY_BASE) + relative;
+	else
+		m_download_url = m_base_url + relative;
 
 	if (m_rules.empty())
 	{
diff --git a/logic/minecraft/RawLibrary.cpp b/logic/minecraft/RawLibrary.cpp
index 7e0ebff0..3351268a 100644
--- a/logic/minecraft/RawLibrary.cpp
+++ b/logic/minecraft/RawLibrary.cpp
@@ -13,20 +13,20 @@ RawLibraryPtr RawLibrary::fromJson(const QJsonObject &libObj, const QString &fil
 	}
 	out->m_name = libObj.value("name").toString();
 
-	auto readString = [libObj, filename](const QString & key, QString & variable)
+	auto readString = [libObj, filename](const QString & key, QString & variable) -> bool
 	{
-		if (libObj.contains(key))
+		if (!libObj.contains(key))
+			return false;
+		QJsonValue val = libObj.value(key);
+
+		if (!val.isString())
 		{
-			QJsonValue val = libObj.value(key);
-			if (!val.isString())
-			{
-				QLOG_WARN() << key << "is not a string in" << filename << "(skipping)";
-			}
-			else
-			{
-				variable = val.toString();
-			}
+			QLOG_WARN() << key << "is not a string in" << filename << "(skipping)";
+			return false;
 		}
+
+		variable = val.toString();
+		return true;
 	};
 
 	readString("url", out->m_base_url);
diff --git a/logic/minecraft/RawLibrary.h b/logic/minecraft/RawLibrary.h
index f5a28c61..583c34d2 100644
--- a/logic/minecraft/RawLibrary.h
+++ b/logic/minecraft/RawLibrary.h
@@ -28,10 +28,11 @@ public: /* methods */
 	
 public: /* data */
 	QString m_name;
-	QString m_base_url = "https://" + URLConstants::LIBRARY_BASE;
+	QString m_base_url;
+
 	/// type hint - modifies how the library is treated
 	QString m_hint;
-	/// absolute URL. takes precedence over m_download_path, if defined
+	/// DEPRECATED: absolute URL. takes precedence over m_download_path, if defined
 	QString m_absolute_url;
 
 	bool applyExcludes = false;
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 3b2b8b74..d56988e0 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -22,6 +22,7 @@ endmacro()
 # Tests START #
 
 add_unit_test(pathutils tst_pathutils.cpp)
+add_unit_test(gradlespecifier tst_gradlespecifier.cpp)
 add_unit_test(userutils tst_userutils.cpp)
 add_unit_test(inifile tst_inifile.cpp)
 add_unit_test(UpdateChecker tst_UpdateChecker.cpp)
diff --git a/tests/tst_gradlespecifier.cpp b/tests/tst_gradlespecifier.cpp
new file mode 100644
index 00000000..69dd54f7
--- /dev/null
+++ b/tests/tst_gradlespecifier.cpp
@@ -0,0 +1,77 @@
+#include <QTest>
+#include "TestUtil.h"
+
+#include "logic/minecraft/GradleSpecifier.h"
+
+class GradleSpecifierTest : public QObject
+{
+	Q_OBJECT
+private
+slots:
+	void initTestCase()
+	{
+
+	}
+	void cleanupTestCase()
+	{
+
+	}
+
+	void test_Positive_data()
+	{
+		QTest::addColumn<QString>("through");
+
+		QTest::newRow("3 parter") << "org.gradle.test.classifiers:service:1.0";
+		QTest::newRow("classifier") << "org.gradle.test.classifiers:service:1.0:jdk15";
+		QTest::newRow("jarextension") << "org.gradle.test.classifiers:service:1.0@jar";
+		QTest::newRow("jarboth") << "org.gradle.test.classifiers:service:1.0:jdk15@jar";
+		QTest::newRow("packxz") << "org.gradle.test.classifiers:service:1.0:jdk15@jar.pack.xz";
+	}
+	void test_Positive()
+	{
+		QFETCH(QString, through);
+
+		QString converted = GradleSpecifier(through);
+		
+		QCOMPARE(converted, through);
+	}
+
+	void test_Path_data()
+	{
+		QTest::addColumn<QString>("spec");
+		QTest::addColumn<QString>("expected");
+
+		QTest::newRow("3 parter") << "group.id:artifact:1.0" << "group/id/artifact/1.0/artifact-1.0.jar";
+		QTest::newRow("doom") << "id.software:doom:1.666:demons@wad" << "id/software/doom/1.666/doom-1.666-demons.wad";
+	}
+	void test_Path()
+	{
+		QFETCH(QString, spec);
+		QFETCH(QString, expected);
+
+		QString converted = GradleSpecifier(spec).toPath();
+		
+		QCOMPARE(converted, expected);
+	}
+	void test_Negative_data()
+	{
+		QTest::addColumn<QString>("input");
+
+		QTest::newRow("too many :") << "org:gradle.test:class:::ifiers:service:1.0::";
+		QTest::newRow("nonsense") << "I like turtles";
+		QTest::newRow("empty string") << "";
+		QTest::newRow("missing version") << "herp.derp:artifact";
+	}
+	void test_Negative()
+	{
+		QFETCH(QString, input);
+
+		GradleSpecifier spec(input);
+		QVERIFY(!spec.valid());
+		QCOMPARE(spec.operator QString(), QString("INVALID"));
+	}
+};
+
+QTEST_GUILESS_MAIN_MULTIMC(GradleSpecifierTest)
+
+#include "tst_gradlespecifier.moc"