Developers

Fermium is an MCP server first. Point any MCP client at https://fermium.app/mcp, sign in once in the browser, and the tools below are available to your agent. The REST API is what the web app uses; the same document model sits under both.

Start here

MCP server

Every tool at https://fermium.app/mcp, with parameters, response shape and example prompts.

REST API

The endpoints behind the web app: documents, files, tokens, workspace, billing, domains.

Authentication

OAuth 2.1 with PKCE and dynamic client registration for MCP clients; bearer tokens; cookie sessions.

Headless tokens

Long-lived dsk_ tokens for CI and scripts, minted in the app and sent as a Bearer header.

Reference

Custom domains API

Add a hostname, read the DNS records, verify, set it as the link host, remove it.

Webhooks

Outbound workspace events signed per endpoint, with retries and a delivery log. Business plan and above.

Rate limits and quotas

What the server enforces per user and per IP, and the size caps by plan.

Errors

Status codes and JSON error shapes from the API, the MCP server and the OAuth endpoints.

Changelog

What shipped, by date.

Connect an agent

1. Add Fermium
Run in a terminal with Codex CLI installed.
codex mcp add fermium --url https://fermium.app/mcp
Using the app or IDE? See setup options.
2. Sign in to Fermium
If the add command already signed you in, continue to step 3. Otherwise, run:
codex mcp login fermium
Finish signing in and approve access in your browser. No token to copy.
3. Start a new chat
Open a new Codex session. Use /mcp to check Fermium is connected, then try this prompt:
Use Fermium's usage_guide to show me what I can do.

Full Codex guide Other clients