Universal Modder Not Working? Installation and Game Diagnostics

Start at the stage that failed. Keep the exact error, command, terminal environment and relevant versions before changing tools or files. The agent integration, Python CLI, optional asset service and game loader have separate checks.

Installation errors

Error or symptom	Diagnostic
Gemini cannot start Git: `spawn git ENOENT`	Check Git and the working directory
Gemini reports `Configuration file not found at` a path ending in `gemini-extension.json`	Check the missing-manifest case
The shell reports `um: command not found` or `um is not recognized`	Check the CLI installation and PATH

The Gemini Git failure is tracked in issue #109. The missing-manifest page covers issue #13 and its fix; a current plugin-discovery problem can still have a different cause.

Agent plugin discovery

If a skill is absent without a specific error, open the workspace that belongs to your installation route, inspect the agent's installed/enabled integrations and start a fresh session. Follow your agent's installation page for its own discovery commands. The plugin discovery guide separates skills, the terminal CLI and fal authentication so you can identify which check actually failed.

For clone-based use, the repository folder and agent configuration need to be in the opened workspace. A clone in another directory or an executable on PATH is not enough for the agent to load mod-any-game.

CLI errors

Begin with local help and version output:

text

Select code

um --version
um --help

You can select the code to copy it manually.

If um is missing, use the PATH diagnosis. If it starts but rejects an argument, inspect the most specific help command, such as um backup restore --help. The Universal Modder um CLI reference covers version 0.2.0 syntax for all ten command groups.

A Python traceback after command discovery points to a different stage. Preserve its final error and the command that triggered it rather than repeatedly reinstalling the skill.

Asset and media errors

Error	Diagnostic
`um: FAL_KEY is not set.`	Set the key in the process that needs it
`FileNotFoundError` naming `ffmpeg`	Check the video tools in the correct environment

Both are local dependency failures in Universal Modder 0.2.0: the command stops before any network request or media processing. Fixing them lets the command start; check the generation or recording result separately.

For local images, um comfy uses your running ComfyUI server without a fal key. For hosted generation, read optional asset setup before starting a paid job.

Minecraft errors

Symptom	Diagnostic
Incompatible mods, loader dependency errors or `UnsupportedClassVersionError`	Compare game, loader, dependency and Java versions
The mod or new block does not appear	Check the instance, JAR and registration

The Minecraft modding guide and fixed-version block exercise list their own version requirements. Keep the edition, loader and game version attached to any check you reuse.

Verify a fix

Repeat the original failed check in the same environment. If its output changes to a different error, record that new failure and diagnose its stage. Keep existing PATH entries, shared dependencies, other mods and saves intact.

Once the tool works, return to the Universal Modder tutorial and complete its next checkpoint. A successful command, build and game action are different observations. The prompt examples include ways to ask an agent for a focused diagnosis with the actual error.

Still need help?

Prepare the failed action, exact redacted error, versions, platform and checks you have tried. Open an issue on the GitHub issue tracker or ask in the project Discord for toolkit help. Use contact for an error in this site's instructions. Do not include API keys or private save data.