diff --git a/fabric-client-gametest-api-v1/src/client/java/net/fabricmc/fabric/impl/client/gametest/ClientGameTestPreLaunch.java b/fabric-client-gametest-api-v1/src/client/java/net/fabricmc/fabric/impl/client/gametest/ClientGameTestPreLaunch.java
new file mode 100644
index 0000000000..2a60dba5cb
--- /dev/null
+++ b/fabric-client-gametest-api-v1/src/client/java/net/fabricmc/fabric/impl/client/gametest/ClientGameTestPreLaunch.java
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.impl.client.gametest;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.apache.commons.io.file.PathUtils;
+import org.jetbrains.annotations.Nullable;
+
+import net.fabricmc.loader.api.FabricLoader;
+import net.fabricmc.loader.api.entrypoint.PreLaunchEntrypoint;
+
+public class ClientGameTestPreLaunch implements PreLaunchEntrypoint {
+	private static final String MARKER_FILE_NAME = ".client_gametests_rundir";
+	private static final Set<String> CLEAN_DENY_LIST = Set.of(".fabric", "mods", "logs", "eula.txt");
+
+	@Override
+	public void onPreLaunch() {
+		Boolean isClientGametestRunDir = detectClientGametestRunDir();
+		boolean isClientGametestEnvironment = System.getProperty("fabric.client.gametest") != null;
+
+		if (isClientGametestRunDir != null && isClientGametestEnvironment != isClientGametestRunDir) {
+			if (isClientGametestEnvironment) {
+				throw new RuntimeException("Running a client gametest in a non-client-gametest run directory. Please use separate run directories for client gametests");
+			} else {
+				throw new RuntimeException("Running a non-client-gametest in a client gametest run directory. Please use separate run directories for client gametests");
+			}
+		}
+
+		if (isClientGametestEnvironment) {
+			cleanRunDir();
+		}
+	}
+
+	@Nullable
+	private static Boolean detectClientGametestRunDir() {
+		Path gameDir = FabricLoader.getInstance().getGameDir();
+
+		if (Files.exists(gameDir.resolve(MARKER_FILE_NAME))) {
+			return true;
+		}
+
+		try (Stream<Path> files = Files.list(FabricLoader.getInstance().getGameDir())) {
+			boolean isNonGametestDir = files.anyMatch(file -> !CLEAN_DENY_LIST.contains(file.getFileName().toString()));
+			return isNonGametestDir ? false : null;
+		} catch (IOException e) {
+			throw new RuntimeException("Error detecting client gametest directory", e);
+		}
+	}
+
+	private static void cleanRunDir() {
+		try {
+			Path gameDir = FabricLoader.getInstance().getGameDir();
+			List<Path> filesToDelete;
+
+			try (Stream<Path> files = Files.list(gameDir)) {
+				filesToDelete = files.filter(file -> !CLEAN_DENY_LIST.contains(file.getFileName().toString())).toList();
+			}
+
+			for (Path path : filesToDelete) {
+				PathUtils.delete(path);
+			}
+
+			Files.createFile(gameDir.resolve(MARKER_FILE_NAME));
+		} catch (IOException e) {
+			throw new RuntimeException("Error cleaning gametest directory", e);
+		}
+	}
+}
diff --git a/fabric-client-gametest-api-v1/src/client/resources/fabric.mod.json b/fabric-client-gametest-api-v1/src/client/resources/fabric.mod.json
index 4de3a7388f..2dd2f8e2b5 100644
--- a/fabric-client-gametest-api-v1/src/client/resources/fabric.mod.json
+++ b/fabric-client-gametest-api-v1/src/client/resources/fabric.mod.json
@@ -20,6 +20,11 @@
     "fabric-resource-loader-v0": "*"
   },
   "description": "Allows registration of client game tests.",
+  "entrypoints": {
+    "preLaunch": [
+      "net.fabricmc.fabric.impl.client.gametest.ClientGameTestPreLaunch"
+    ]
+  },
   "mixins": [
     "fabric-client-gametest-api-v1.mixins.json"
   ],