markmnl/fmsg-mcp

An MCP server that gives any AI agent its own
fmsg address: send messages, follow threads, react, exchange
attachments and wait for replies, through a deployed
fmsg Web API. Connect through stdio in hosts such as
Claude Code, Claude Desktop, Cursor and VS Code, or through HTTP using API-key headers or configured OAuth.
Use your choice of fmsg hosting provider, or self-host. No hosting provider or identity provider
is built in.
- **stdio** for local hosts: one address per server process, configured by two environment variables.
- **Streamable HTTP** for shared or remote deployments: one endpoint serving many users, each
authenticated by their own fmsg API key or OAuth connection.
- The fmsg Web API client is exported for reuse: import { FmsgClient } from "@markmnl/fmsg-mcp/client".
1. Choose a connection
OAuth: connect and sign in
Get an OAuth-enabled MCP URL from your fmsg hosting provider, add it to your AI host, and sign in.
You do not need an API key or a local installation for this connection. Your AI host must support
the authorization server's client registration method; see OAuth onboarding.
Operators can enable this with HTTP OAuth.
API key: use locally or over HTTP
You send as an fmsg address, authenticated by an API key (fmsgk_…) issued by your fmsg host:
- **Using a hosting provider?** Create an account with an fmsg hosting provider and obtain an
API URL and API key for the address your agent will use.
- **Self-hosting?** Run the stack with fmsg-docker and issue
a key with fmsg-webapi api-key create.
Use the API URL and key for local installation below, or use your provider's API-key MCP endpoint
with an Authorization: Bearer fmsgk_... header. The endpoint must use the fmsg Web API that accepts
your key.
MCP Registry
Find io.github.markmnl/fmsg-mcp in the official MCP Registry.
The listing offers local npm installation and configurable remote connections for OAuth or API keys.
For a remote connection, supply the MCP endpoint from your fmsg hosting provider or your own deployment;
the registry input takes its hostname and path without the https:// prefix, such as mcp.example.com/mcp.
OAuth sign-in is discovered from that endpoint; the API-key option additionally asks for your key.
If your AI host cannot configure registry URL templates, add the full MCP URL directly instead.
2. Install
Requires Node.js 22 or later.
Claude Code
Then in any session: *"Send @bob@example.com a note about the release"*, *"What's in my fmsg inbox?"*,
*"Wait for Bob's reply and answer it"*. /fmsg:chat, /fmsg:reply and /fmsg:send_file are available as prompts.
Claude Desktop, Cursor, VS Code and other stdio hosts
Add a server entry with the same command; only the config file differs:
(Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code: .vscode/mcp.json
under "servers" with "type": "stdio".)
Remote (Streamable HTTP) mode
Run one server for many users. Each client sends **its own** fmsg API key as a bearer token; the
server exchanges it at the fmsg host and acts as that address. FMSG_API_KEY must not be set.
The MCP endpoint is /mcp; /healthz reports liveness. Use a client that supports an explicitly
configured Authorization: Bearer fmsgk_... header. Each caller supplies its own key; a shared
header means a shared fmsg identity. For browser sign-in without user API keys, configure
HTTP OAuth: the operator supplies an issuer, resource URI and exchange client.
Users add the public MCP URL in a host supporting that issuer's client registration method.
FMSG_MCP_AUTH_MODE=oauth+api-key accepts both OAuth and API-key callers on the same URL.
For Claude Code over HTTP:
Deploy behind a TLS-terminating reverse proxy and set FMSG_MCP_ALLOWED_HOSTS to the public hostname
when binding to a non-loopback address; startup fails without it. Browser clients on another origin
also need FMSG_MCP_ALLOWED_ORIGINS containing exact origins, such as https://app.example.com.
For loopback binds, loopback browser origins on any port work by default, including MCP Inspector
at http://localhost:6274. Setting an explicit origin list replaces that loopback default.
Allowed preflights need no credentials; actual MCP requests always require authentication.
wait_for_message holds a request open for up to