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

# Authentication

> Workspace API keys and OAuth tokens.

Every endpoint takes one of:

| Scheme | How to send it | Access |
| - | - | - |
| Workspace API key | `api-key: <key>` header. Find it in Letterdrop under Settings → Integrations → API Key. | Full access to the workspace. |
| MCP OAuth token | `Authorization: Bearer <token>` | The scopes granted when the token was issued. |

### Scopes

| Scope | Grants |
| - | - |
| `mcp.read` | Every endpoint in this API (all are reads). Part of every token. |
| `mcp.write` | Actions elsewhere in Letterdrop (sending messages, changing workflows). Not needed here. |

A credential in the query string is rejected. A credential only ever reads its own workspace.


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