← DEVLOG · 2026.09.02 · release
uefn-mcp-pro: our AI tooling for UEFN is open source
We’ve been building Fortnite islands with an AI agent in the loop since March 2026, when we shipped our first open-source MCP server for UEFN. In August, Epic made the workflow official: UEFN 42.00 ships with a built-in Unreal MCP. Today we’re releasing what those five months of production taught us: uefn-mcp-pro — a server that sits on top of Epic’s official one and adds everything it doesn’t expose. MIT, free, for every creator.
The short version: Claude Code, Cursor or Codex works inside UEFN like a junior developer with a keyboard. It writes and compiles Verse, places and wires devices, builds UI, runs playtests, reads the logs and fixes its own errors. It has been the backbone of the Three Suns pipeline for months — every custom NPC, shop screen and combat room in that project went through it.
What the agent gets
- One flat toolbox of 58 actions: Verse files and build diagnostics, Creative devices and their event bindings, Scene Graph entities, bulk actor/asset operations, viewport screenshots, playtest sessions and their client logs.
- Pass-through to Epic’s official server — all ~400 tools of the built-in Unreal MCP are reachable through a single search interface, so the agent doesn’t drown in a 44 KB schema.
- A visual feedback loop: the agent screenshots the viewport to see what it just built. Every operation is one Ctrl+Z.
The speed fix nobody else ships
Here’s our favorite number. UEFN throttles itself to 3 updates per second when its window is in the background — which is exactly where it sits while an AI works. Every action used to wait ~333 ms for the next tick. We turn that throttle off: actions now complete in 10–50 ms with the editor unfocused. Multiply across the hundreds of calls in an edit → build → playtest loop and the whole iteration runs 15–30× faster.
The agent never says “done” on a red build
The other half of the work is visibility. uefn-mcp-pro parses and hands the agent everything the editor knows: the editor log, Verse compiler errors with file and line, the playtest session’s client log, Python errors. If the build is red, the agent sees it — and knows where to look.
Ours vs. Epic’s built-in MCP
| Epic’s Unreal MCP | uefn-mcp-pro | |
|---|---|---|
| Tools for the agent | 3 generic meta-tools | 58 purpose-built + search over Epic’s |
| Speed with editor in background | ~333 ms per action | 10–50 ms |
| Bulk actor/asset ops, screenshots, editor Python | — | yes |
| What the AI sees on errors | editor log | Verse diagnostics, playtest logs, Python errors — parsed |
| Custom tools | not allowed | any Python via a sidecar |
To be clear: this is built on top of the official server, not against it. Epic’s MCP drives the game — it compiles Verse, spawns Scene Graph entities, runs live sessions. Ours makes the agent fast and observant around it, and follows Epic’s API as it evolves.
Grab it
Everything is on GitHub, MIT-licensed: github.com/novikit/uefn-mcp-pro — install guide, full tool reference and our research notes on UEFN internals are in the repo. It evolved from our first server, uefn-mcp-server, which stays up for reference.
A tutorial series is in progress: Building a Fortnite island with an AI agent. If you wire this into your own island — show us in Discord, we want to see what breaks first.