# OpenAPI document · Elysium API · Femtos

> The OpenAPI 3.1 contract of every REST call, public.

- Base URL: `https://api.femtos.xyz/v1` (REST) · `wss://api.femtos.xyz/v1/ws` (WebSocket) · MCP: `https://api.femtos.xyz/mcp`
- Auth: `Authorization: Bearer $FEMTOS_KEY` (or `X-API-KEY: $FEMTOS_KEY`). Free key: https://femtos.xyz/accounts/ (browser), or with
  no browser: `GET https://femtos.xyz/accounts/agent/challenge`, solve its proof of work, then `POST https://femtos.xyz/accounts/agent/signup`
  (https://femtos.xyz/agents.md#agent-onboarding)
- Decimals are exact strings, times Unix milliseconds, addresses lowercase `0x`
- Whole API in one file: https://femtos.xyz/agents.md · OpenAPI: https://api.femtos.xyz/v1/openapi.json · Index: https://femtos.xyz/llms.txt
- Page with live calls: https://femtos.xyz/hypercore/openapi

## OpenAPI document — GET `/v1/openapi.json`

The OpenAPI 3.1 contract of every REST call, public.

```bash
curl -H "Authorization: Bearer $FEMTOS_KEY" "https://api.femtos.xyz/v1/openapi.json"
```

| Field | Type | Meaning |
|---|---|---|
| `paths` | object | every operation |
| `components.schemas` | object | response shapes |
| `x-websocket.channels` | object[] | WebSocket channels |

## Related (Reference)

- [Blocks stream](https://femtos.xyz/elysium/ws-blocks.md): Each new Elysium block header, from our node.
- [Freshness](https://femtos.xyz/elysium/status.md): Head and lag of each layer, measured now.
- [Check your key](https://femtos.xyz/elysium/whoami.md): Answers the name your key is registered under, its tier, billing state and the limits in force.

All Elysium endpoints: https://femtos.xyz/elysium.md