diff --git a/src/main/java/net/fabricmc/loader/impl/game/GameProviderHelper.java b/src/main/java/net/fabricmc/loader/impl/game/GameProviderHelper.java
index a55819455..2b3cd531a 100644
--- a/src/main/java/net/fabricmc/loader/impl/game/GameProviderHelper.java
+++ b/src/main/java/net/fabricmc/loader/impl/game/GameProviderHelper.java
@@ -55,6 +55,8 @@
 import net.fabricmc.tinyremapper.TinyUtils;
 
 public final class GameProviderHelper {
+	private static final boolean DEVELOPMENT_DEOBF_GAME_JAR = System.getProperty(SystemProperties.DEVELOPMENT_DEOBF_GAME_JAR) != null;
+
 	private GameProviderHelper() { }
 
 	public static Path getCommonGameJar() {
@@ -163,7 +165,7 @@ public static Map<String, Path> deobfuscate(Map<String, Path> inputFileMap, Stri
 	public static Map<String, Path> deobfuscate(Map<String, Path> inputFileMap, String gameId, String gameVersion, Path gameDir, FabricLauncher launcher, String sourceNamespace) {
 		Log.debug(LogCategory.GAME_REMAP, "Requesting deobfuscation of %s", inputFileMap);
 
-		if (launcher.isDevelopment()) { // in-dev is already deobfuscated
+		if (launcher.isDevelopment() && !DEVELOPMENT_DEOBF_GAME_JAR) { // in-dev is already deobfuscated
 			return inputFileMap;
 		}
 
diff --git a/src/main/java/net/fabricmc/loader/impl/launch/MappingConfiguration.java b/src/main/java/net/fabricmc/loader/impl/launch/MappingConfiguration.java
index ca4a156a7..961c30021 100644
--- a/src/main/java/net/fabricmc/loader/impl/launch/MappingConfiguration.java
+++ b/src/main/java/net/fabricmc/loader/impl/launch/MappingConfiguration.java
@@ -20,6 +20,8 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.JarURLConnection;
+import java.net.MalformedURLException;
+import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
 import java.util.List;
@@ -42,6 +44,8 @@
 import net.fabricmc.mappingio.tree.MemoryMappingTree;
 
 public final class MappingConfiguration {
+	private static final String MAPPINGS_PATH = System.getProperty(SystemProperties.MAPPINGS_PATH, null);
+	private static final String TARGET_NAMESPACE = System.getProperty(SystemProperties.TARGET_NAMESPACE, null);
 	private static final boolean FIX_PACKAGE_ACCESS = System.getProperty(SystemProperties.FIX_PACKAGE_ACCESS) != null;
 
 	private boolean initializedMetadata;
@@ -91,6 +95,10 @@ public MappingTree getMappings() {
 	}
 
 	public String getTargetNamespace() {
+		if (TARGET_NAMESPACE != null) {
+			return TARGET_NAMESPACE;
+		}
+
 		return FabricLauncherBase.getLauncher().isDevelopment() ? "named" : "intermediary";
 	}
 
@@ -178,7 +186,17 @@ private void initializeMappings() {
 
 	@Nullable
 	private URLConnection openMappings() {
-		URL url = MappingConfiguration.class.getClassLoader().getResource("mappings/mappings.tiny");
+		URL url;
+
+		if (MAPPINGS_PATH != null) {
+			try {
+				url = new URL(MAPPINGS_PATH);
+			} catch (MalformedURLException ex) {
+				url = null;
+			}
+		} else {
+			url = MappingConfiguration.class.getClassLoader().getResource("mappings/mappings.tiny");
+		}
 
 		if (url != null) {
 			try {
diff --git a/src/main/java/net/fabricmc/loader/impl/util/SystemProperties.java b/src/main/java/net/fabricmc/loader/impl/util/SystemProperties.java
index 658767bd5..53d77189b 100644
--- a/src/main/java/net/fabricmc/loader/impl/util/SystemProperties.java
+++ b/src/main/java/net/fabricmc/loader/impl/util/SystemProperties.java
@@ -19,6 +19,8 @@
 public final class SystemProperties {
 	// whether fabric loader is running in a development environment / mode, affects class path mod discovery, remapping, logging, ...
 	public static final String DEVELOPMENT = "fabric.development";
+	// runtime deobf game jar although it is in development
+	public static final String DEVELOPMENT_DEOBF_GAME_JAR = "fabric.development.deobfGameJar";
 	public static final String SIDE = "fabric.side";
 	// skips the embedded MC game provider, letting ServiceLoader-provided ones take over
 	public static final String SKIP_MC_PROVIDER = "fabric.skipMcProvider";
@@ -42,6 +44,10 @@ public final class SystemProperties {
 	public static final String REMAP_CLASSPATH_FILE = "fabric.remapClasspathFile";
 	// class path groups to map multiple class path entries to a mod (paths separated by path separator, groups by double path separator)
 	public static final String PATH_GROUPS = "fabric.classPathGroups";
+	// direct use a tiny file as mappings for mapping configuration
+	public static final String MAPPINGS_PATH = "fabric.mappingsPath";
+	// define the target namespace for mapping configuration
+	public static final String TARGET_NAMESPACE = "fabric.targetNamespace";
 	// enable the fixing of package access errors in the game jar(s)
 	public static final String FIX_PACKAGE_ACCESS = "fabric.fixPackageAccess";
 	// system level libraries, matching code sources will not be assumed to be part of the game or mods and remain on the system class path (paths separated by path separator)