Offprompt MCP Server

offprompt

offprompt lets a coding agent ask you for a secret and have it land where the project needs it, without the value passing through the model.

Agents need API keys. Paste one into the chat and it goes into the model's context, the transcript on disk and the provider's logs, and stays there. offprompt gives the agent another way to ask: a tool call that opens a page in your browser, from which the value goes straight into the file. The transcript only ever sees the key's name.

How it works

1. The agent asks. It calls collect_secret with every key it needs, why it needs them, and the file they go in, then waits inside the call.
2. A page opens on 127.0.0.1 in your browser. It says which agent is asking, what for, and which file it writes to. Each field checks its value as you type, paste or import it, and links to where the key is made.
3. The file is written. offprompt answers the agent with the key names, the file and a four-emoji fingerprint, the same four your page shows. From then on the agent reads the values from the environment by name.

When the agent runs in a cloud sandbox, it gives you a link to the page instead. The page reaches you through a Cloudflare tunnel, and your browser encrypts the values first, to a key only the sandbox holds.

The page itself can be tried at offprompt.dev/playground.

Install

In a project's folder:

npx offprompt init

That puts the server in the project as tools/offprompt/mcp.mjs, one file that runs on node alone, and declares it in the project config of each agent found on your machine. Commit those files together with tools/offprompt/, and everyone on the project gets offprompt, as does every cloud sandbox that clones it.

To have offprompt in every project you open instead, install it for yourself:

npx offprompt init -g

npx offprompt list        # every agent, whether it was found, and how offprompt reaches it
npx offprompt remove      # out of this project
npx offprompt remove -g   # out of every agent that has it

offprompt runs on Node 22 or later. Installation covers choosing agents with --agent, and updating.

Agents

offprompt is an MCP server, so any agent that speaks MCP can use it. init sets these up:

Claude Code asks once before it starts a server a project declares. Codex and Pi read a project's config only in a project you trust. Agents has each one in detail.

Manual MCP config

Any other MCP client, Cline among them, can start offprompt from npm:

{
  "mcpServers": {
    "offprompt": {
      "command": "npx",
      "args": ["-y", "offprompt", "mcp"]
    }
  }
}

Cline also needs the project as cwd, since it names no project to the servers it starts. llms-install.md has the entry for Cline, and steps an agent can follow to install offprompt.

Documentation

docs.offprompt.dev has the rest: what the agent can ask for, the page, every provider offprompt knows and the checks on its keys, the tools, cloud sandboxes and troubleshooting. offprompt.dev shows offprompt at work.

Security

A value goes from your browser to offprompt to the file, and never through the model, the transcript, or a tool's arguments and results. offprompt does not guard the file once it is written, or protect against another program running as you: the threat model says what it covers, and SECURITY.md how to report a problem.

What offprompt runs and reaches:

• A server on 127.0.0.1, which serves the page and takes the write. The page loads nothing from the network.
• Your browser, opened with the platform's URL handler, never a shell: open on macOS, xdg-open on Linux, rundll32 url.dll,FileProtocolHandler on Windows. The agent's host is offered the page first.
• In a cloud sandbox, cloudflared, to reach the page through a Cloudflare quick tunnel that carries only ciphertext. It uses a cloudflared already on PATH, or downloads a pinned release from Cloudflare's GitHub releases once and checks its SHA-256 before running it.

It sends nothing to us, keeps no values once they are written, and collects no telemetry.

Development

A pnpm workspace, on Node 22.13 or later. From a checkout, pnpm install, then pnpm agents --project ~/projects/some-project installs offprompt into a project the way npx offprompt init does. CONTRIBUTING.md has the tests, the layout and how to add a provider.

Licence

MIT, for everything in this repository. The parts that are other people's work keep their own terms, listed in packages/offprompt/THIRD_PARTY_NOTICES.md for the server, the packages bundled into it and the page it serves, in apps/site/THIRD_PARTY_NOTICES.md for offprompt.dev and in apps/docs/public/third-party-notices.txt for docs.offprompt.dev.