Unreal from Codex: Unreal MCP setup, a session contract and a tested asset pipeline for coding agents

What you end up with

Your agent works in a sandbox folder from a written objective, every write is checked and logged, nothing destructive or bulk runs without your yes, and every imported prop has a license, a triangle count and an approval for that exact file.

What you get

• 21 sections in one .md file
• Unreal MCP setup: plugins, starting the server, client configs and the write-once Codex entry
• Connection notes for Codex, Claude Code, Grok Bot and Hermes, keeping the server on your own machine
• mcp_probe.py: checks the server answers and lists its tools without calling any
• SESSION.md: objective, leave-out list, checkpoint commit, engine version and triangle budget
• Five risk tiers and an approvals ledger tied to file hashes, with a separate release yes
• An action log format with a verify result for every call, and recovery steps for restarts, stale tools, compiles and timeouts
• blender_prep.py: headless cleanup with joined parts, applied transforms, bottom-center origin, a triangle cap and a prep report
• ue_import.py: imports only approved, unchanged files into /Game/_Agent, never replaces, with a dry run
• ue_check.py: fifteen read-only checks, with a fixture builder and the expected output
• A rules block for any harness, ten prompts and a failure table
• A look at five Unreal MCP tools and plugins, with sources

Who it is for

Unreal 5.8 developers and technical artists who want a coding agent doing editor work and asset imports, and want to know exactly what it changed, with their yes before anything destructive or anything that leaves the machine.

Works with

Solid chips: the agent is named in this listing's own tools list. Dashed chip: Plain Markdown, so it also pastes into other agents such as Grok Bot, Hermes, OpenClaw or Muse. We list those as compatible by format only, not as tested.

Tools needed

Cost to run: The pack is the only purchase. Unreal Engine, Blender and Python are free to start; model usage and generators such as Tripo or Meshy are billed by those vendors.
Time to result: Connected, probed and through a first read-only session in about an hour

How it works

1. Test the check

   Save the scripts from the file, run make_fixture.py and run ue_check.py on the three fixture folders.

   Expected: 15 findings on seeded, 0 on fixed, 1 on broken-uproject; exit 2 on a missing folder.

2. Turn on the server

   Commit the project, enable Model Context Protocol and All Toolsets, start the server and generate the client config for your agent.

   Expected: python3 mcp_probe.py prints the server name and its tools, exit 0.

3. Write the session

   Copy the Agent and Pipeline folders, create /Game/_Agent, and fill SESSION.md with the engine, the checkpoint commit, the objective and the leave-out list.

   Expected: ue_check.py shows no U02 to U05 findings.

4. Run a read-only session, then one small edit

   Add the rules block, use prompt 2 to map the level with tier 0 calls, then prompt 4 for one tier 1 edit you can see.

   Expected: Every call has a row in actions.csv with a verify result, and the edit reads back as asked.

5. Bring in one prop

   Run blender_prep.py on a model in Pipeline/raw, approve the FBX by its hash, run ue_import.py with --dry-run, then for real in the editor.

   Expected: The asset is in /Game/_Agent/Imports, its bounds match size_cm, and ue_check.py prints 0 findings.

Sample prompt from the pack

Read Agent/SESSION.md. Using tier 0 calls only, list the actors in the level named in the objective, grouped by class, with their locations.
Log each call in Agent/actions.csv with what you saw.

I want to rename every texture in {folder} to the T_ prefix. Do not do it yet.
List the old and new names, the number of assets, the referencers you found and how to undo, then ask me.

Free preview of the file

# Unreal from Codex: Unreal MCP setup, a session contract and a tested asset pipeline for coding agents

Version 1.0, 2026-10-28. By PaperChaseWebb. Works with Codex, Claude Code, Grok Bot and Hermes. Plain Markdown, five Python 3 scripts and a fixture builder, tested as described in section 14. The Blender step was run headless on Blender 5.2.3 LTS. The checker, the probe, the import dry run and the free sample checker were run on Linux against a seeded fixture and a mock MCP server. The Unreal Editor steps were not run in Unreal for this release, and each one is marked where it appears.

Unreal Engine 5.8 puts a lot of power one sentence away from your agent. Its Unreal MCP plugin lets a coding agent list actors, change materials, spawn things, run editor Python and, with the wrong prompt, delete folders. This pack is how to connect Codex (or Claude Code, Grok Bot or Hermes) to that server and keep the session boring: a written objective, a commit before the agent touches anything, a log of every tool call with a verify result, and your yes before anything destructive, bulk, or anything that leaves your machine.

The second half is the asset path most people try next: a model from Tripo, Meshy or your own Blender file goes through a headless Blender cleanup, gets a license row and a hash, waits for your approval, and only then is imported into a sandbox folder in your project. A read-only checker, ue_check.py, reads the project and tells you in fifteen checks where the sess

Worth knowing

• The Unreal MCP plugin is labeled experimental by Epic in Unreal Engine 5.8, and tool names can change between builds. List and describe the tools at the start of every session.
• The Unreal Editor steps were not run in Unreal for this release. They follow Epic's 5.8 documentation and a public Codex setup tested on 5.8.3 under Windows. Start with a read-only session.
• Keep the MCP server on 127.0.0.1. Do not open its port to your network or the internet to reach a remote agent.
• Read your generator's current terms before using its models commercially, and write them in the license column.
• On 2026-10-28, ue_check.py reported the fifteen expected findings on the seeded fixture, 0 on the fixed one and 1 on the broken project file, with file hashes unchanged and exit 2 on a missing folder; blender_prep.py ran headless on Blender 5.2.3, refused over the cap, decimated to 4,850 triangles when asked and refused to overwrite; the import dry run planned one import and refused a changed file; the probe passed against a mock MCP server. Run the tests on your own machine first.

Details

Version 1.0 · Updated Oct 28, 2026 · Markdown version of this page
License: Use on your own projects and on installs you do for clients and teams. Do not resell or republish the pack itself. Download terms

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