MMCP

https://github.com/mattjesmc/MMCP for download. No upload here because mod allows modifying code and assets live. Which is not allowed on curseforge.

An MCP toolkit for Minecraft. One mod jar (Fabric and NeoForge, dev and production) opens a localhost HTTP bridge into a running game and registers tools on it; an MCP server fronts that bridge for any MCP client. An agent then authors blocks, data, models, entities, structures, screens and worldgen against a game that is actually running, and reads back what it did.

If you are a person, start at wiki/ - one page per kind of modding work, each with an overview, a walkthrough, an example agent session and the traps that cost us the time. If you are an agent, start at mcp-toolkit/README.md, which maps each task to the one document to read. mcp-toolkit/RELEASE.md is the release ledger: what ships, what has been verified on the code that ships, and what is still open - and where a claim rests on a test log, it names the log.

This is release 3: toolkit 0.157.0, MCP server 0.79.0, convention plugin 0.7.0, Minecraft 26.2. A file you save is in the running game a few seconds later, with nothing called. mmcpd is a daemon that hosts the MCP server for every project on the machine - so registering a client is a URL rather than a command and an environment, and your client spawns nothing - and it watches each registered project's src/: a texture, a datapack file, a screen document or a Java method body you write lands by the route that kind of change needs, batched, with an identical rewrite refused before any game is dialled. Every change is a row you can read, on the daemon's feed and as an edit event inside the game, saying what became of it - swapped, refused, not-yet, pending-rebuild. The same daemon now serves a cockpit at /ui/. The stdio server and the in-jar door (POST http://127.0.0.1:<port>/mcp, no Node, nothing to install) are both unchanged and both still supported - mcp-toolkit/docs/platform/HOST_DESIGN.md and IN_JAR_MCP_DESIGN.md have the tables.

The whole probe battery was re-run at this version on 2026-09-14 - 112 files, 950 pass / 1 fail, the one red green on an isolated rerun - and 108 of the 109 files it shares with release 2's battery scored identically, with every difference accounted for: three new probe files and eight new cases in a fourth. No shared file lost a test. That is the evidence this version changed nothing it did not mean to (RELEASE.md 2.11).

License, in short

Read LICENSE; it is written to be read. The summary:

• Free for non-commercial use, with nobody to ask - playing, learning, teaching, research, hobby modding, and building things you give away.
• Anything you author with it is entirely yours. No condition on your mods, assets, data or worlds, and no claim on them.
• Commercial use needs permission first - by or for a business, in anything sold or offered for payment, in paid work or a paid service. A door, not a wall: say what you want to do and ask, before you start rather than after.
• Do not redistribute the jar or the server. Not to a mod site, a mirror, a modpack or a registry. Link people here instead, so that what they download is what was actually released, at the version it claims to be. A modified version that adds real new capability you may pass on, named so it is not mistaken for this one and under these same terms.

If you are unsure which side of a line you are on, that is a question and not a verdict - ask.

Two other things worth knowing before you start

It is a snapshot, not a history. The development workbench is a private repository whose history carries work that is not part of this release; what you see here is its tree at the release version, committed once. There is no commit log to read behind these files.

Windows only, and no permission system. The bridge binds 127.0.0.1 and any local process that can reach the port can drive the game. That is the trust model; there is nothing behind it.

Not an official Minecraft product. Not approved by or associated with Mojang.

The workbench this was cut from

This directory is a WORKBENCH, not a monorepo: several independent Gradle build roots that share one convention plugin and one local Maven repository. The product is the MCP Toolkit; everything else here builds it, tests it, or was its first customer.

If you are a person, start at wiki/ — one page per kind of modding work, each with an overview, a walkthrough, an example agent session and the traps. If you are an agent, start at mcp-toolkit/README.md — it maps each task to the one document or section to read.

What is here

How a mod repository uses this workbench

Sibling checkouts (rocketeer, menagerie, nijntje, villagejobs, …) are separate repositories. Village Jobs was the toolkit's first customer and lived at this root until 2026-09-06; its history before that date is this repository's. Each sibling:

1. applies id 'com.mattmc.mcmod' after Fabric Loom and resolves the plugin and the toolkit from mavenLocal - ./gradlew build in mcp-toolkit/ and in gradle-conventions/ publishes them (mcp-toolkit/EXTENDING.md, Quickstart);
2. carries a .mcp.json that runs mcp-server/index.mjs with MCPTK_URL pointing at ITS bridge port. The port is a per-project constant that names the project (mcp-toolkit/RELEASE_1.md section B0); ./gradlew toolkitStatus prints it;
3. optionally carries .mcptoolkit/loop.json and .claude/agents/*.md for authoring loops (mcp-toolkit/docs/guides/LOOPS.md).

Rules that bite

• Never run gradlew build or :jar while a dev game is running: the game holds the jar. Use tools/rebuild.ps1 for structural changes and hotswap_class for method bodies. The full decision table is the first section of mcp-toolkit/LIVE_MODDING.md.
• One dev game per bridge port. A second rebuild.ps1 on the same port exits 3 instead of killing the first game's cycle; tools/dev-procs.ps1 shows who owns what.
• Live probes (mcp-server/probes/) run against ONE world and each file owns distinct sites. The arbiter is tools/battery.ps1 (sequential); npm run test:live is a concurrent load test.
• Documents cite each other by bare filename (LOOP_KIT_DESIGN.md, section 5). Every UPPER_CASE record name is unique across the tree, so find a cited document by name, not by the directory the citation was written in. The index is mcp-toolkit/docs/README.md.