> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fau.run/agent-docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Federated Agent Use for agents

> Call a user's local mail node without ever holding their inbox credentials.

Federated Agent Use (FAU) lets a remote assistant ask narrow questions about someone's
email. The mail stays on their Mac. You never receive an IMAP password, OAuth token, or
raw mailbox dump.

Public relay for discovery and reachability:

```
https://relay.fau.run
```

Protocol version: **`fau/1`**.

## How it feels

Like email, not like an API key portal:

1. You address a person by email (`user@gmail.com`).
2. The relay tells you how to reach their node (or a decoy that looks the same if they
   are not registered).
3. You open TLS to their node hostname and call MCP tools over `POST /mcp`.
4. Every request is **signed** as your agent domain. Access is decided by **grants** and
   **phone approvals** on their side — not by registering with us.

There is no “sign up your agent with FAU.” Publish keys at
`https://<your-domain>/.well-known/fau-agent` and you can attempt contact.

## What you will implement

| Step                                  | Doc                                                |
| ------------------------------------- | -------------------------------------------------- |
| Resolve an email → node hostname      | [Resolve](/agent-docs/agent-docs/connect/resolve)             |
| Publish agent keys                    | [Identity](/agent-docs/agent-docs/connect/identity)           |
| Sign every `/mcp` request (RFC 9421)  | [Signing](/agent-docs/agent-docs/connect/signing)             |
| Dial the node + MCP session           | [Transport](/agent-docs/agent-docs/connect/transport)         |
| Offline Mac                           | [Offline queue](/agent-docs/agent-docs/connect/offline-queue) |
| Call tools (`ask`, travel, drafts, …) | [Tools](/agent-docs/agent-docs/tools/overview)                |
| Handle approval prompts               | [Approvals](/agent-docs/agent-docs/tools/approvals)           |

## Hard rules

<Warning>
  Never ask the user for Gmail credentials. If your product needs an inbox token, you are
  not using Federated Agent Use.
</Warning>

* Prefer structured tools and `ask` before `get_excerpt`.
* Treat `approval_required` as a normal control flow, not a crash.
* Show the user the **verified agent domain** and the 2-digit **match code** whenever a
  phone prompt fires.
* Expect rate limits, blocks, and denials. Retry with backoff; do not hammer.

## Next

* New to FAU? Start with [Concepts](/agent-docs/agent-docs/concepts), then [Quickstart](/agent-docs/agent-docs/quickstart).
* Integrating now? Jump to [Resolve](/agent-docs/agent-docs/connect/resolve) and [Signing](/agent-docs/agent-docs/connect/signing).