# MCP security

> Keep your Harny keys out of chat, code and commits, and call the MCP server only from places you control.

## Keep keys out of chat, code and commits

Your app key starts with `fsa_`. A person's key starts with `fsk_`. Treat both as passwords. Put them in your secret store or in a `.env` file that your repo ignores. Do not paste them into a chat with an assistant, into source files, or into commit messages.

The `provision_app` answer carries the app key once. Save it right away in your secret store. The console creates app keys as well.

## Use the no-account setup for coding agents

`provision_app` is the MCP tool that makes a new app. It needs no key. Its answer carries the app key once, and the assistant is told to put that key in your secret store and nowhere else.

If your coding agent can run commands, follow https://harny.ai/auth.md instead. One command makes the app and saves its key in `.env` where nobody reads it. The command never shows the key. It prints a claim link that you open later to take ownership of the app. The `get_claim_link` tool gives you a fresh one-time link. It is not an API key.

## Use server-side keys only

Call the MCP server from a server. Do not call it from a browser, and do not ship a key in a web or mobile client.

## How the MCP server checks access

- With no `Authorization` header, the server offers only `provision_app`.
- With `Authorization: Bearer <key>`, the server offers the tools that key may call.
- The server accepts bearer keys and sign-in tokens. A sign-in token is issued only after the app's owner signs in on the Harny console. It lasts an hour, renews with a refresh token that rotates, and works only at the address it was issued for.
- Harny checks every request against the key.
- Calls are scoped to the key's user. A person's key reaches only that person's memory.
- Each app's data is separate, and each person's memory is separate.

## Check what a key reaches

Call `describe` first. It returns what Harny is and what your key reaches, with the tools that key may call and their schemas. Call `diagnose` to see where your Harny connection stands.

`get_setup_bundle` lists key variable names, never key values.

## Calls follow the REST refusals

An MCP call follows the same limits and refusals as the REST route it wraps. If you hit the per-minute limit, the server answers `429` with a `Retry-After` header. Wait for that time before you retry.

## Next

- [MCP keys and access](/docs/mcp/keys-and-access)
- [MCP tools](/docs/mcp/tools)
- [Memory API authentication](/docs/memory-api/authentication)