Build for Fifth Door

Make a game with the editor and coding agent you already use, then publish it to Fifth Door. You get a play URL, hosting, a place on Discover, weekly game jams, and players. You bring any static web game.

How it fits together

The MCP server is for you and your coding agent while you build: it is how a game gets onto Fifth Door and how you manage it afterward. The Platform SDK is for the game while people play it: services it can call instead of building them itself. You need the first. The second is optional.

While you build

Fifth Door MCP

Tools your agent uses to publish a game, update it, list it on Discover, record its gameplay preview, enter it in a jam, and read the SDK docs. Install it once in Cursor, Claude Code, Codex, or any MCP client.

Publish from your editor

While people play

Platform SDK

One client your game creates at runtime: who is playing, saved progress, shared records, multiplayer rooms and presence, in-game LLM calls, daily puzzles, notifications. A game that uses none of this publishes and runs fine without it.

Platform SDK docs

Quickstart

Add the MCP server to your editor

Add to Cursor

Or add to .cursor/mcp.json:

{
  "mcpServers": {
    "fifth-door": {
      "command": "npx",
      "args": ["-y", "@fifth-door/mcp@latest"]
    }
  }
}

2
Sign in
Ask your agent to run login. It shows a short code and a link. Open the link in a browser where you are signed in to Fifth Door, approve, and the session is cached on your machine.

Publish

Tell your agent what you want. Something like this works as-is:

Publish the game in this project to Fifth Door. Use the fifth-door MCP: run login if we are not signed in, then publish_game with the build output directory (or the project root if there is no build step) and sourceDirectory set to the project root. Give me the play URL when it is done.

You get back a play URL. New games are unlisted, so the link works but the game is not on Discover yet.

From there, ask your agent to make the game public, record a gameplay preview for its card, enter it in this week's jam, or add saved progress with the SDK. The MCP guide lists every tool.

What a game needs

A static web game: index.html at the root of the directory you publish, assets referenced by relative path. Any framework or none.
Up to 200 files and 300 MB per game.
Cover art in the bundle, landscape 4:3 with the title drawn into the artwork. Cards show the cover alone.
A play target: portrait phone (the default), landscape phone, desktop, or everywhere.
Authored source travels with the game. If there is a build step, publish the output directory and point sourceDirectory at the project root.

The full list, including what publishing does with your source, is on the MCP guide.

Other ways in

Studio. Describe a game in the browser and Fifth Door's own agent builds and publishes it. Nothing to install. Start in Studio.
CI and scripts. Create an API key on your account page and set FIFTH_DOOR_TOKEN in the MCP config instead of signing in interactively. Details under Sign in on the MCP guide.
Partner API. Hosted agents that cannot run MCP create and iterate games over REST. Muse opens Fifth Door sign-in (OAuth); scripts can use an API key. The Partner API guide is also raw markdown at /docs/partners.md.