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

# A2A agent cards

> A2A-format agent cards for every registry agent, annotated with Backed trust data.

Backed serves [A2A protocol](https://a2a-protocol.org) agent cards so A2A-speaking agents can combine discovery and a trust check in one fetch.

## Backed's own card

```bash theme={null}
curl https://api.usebacked.ai/.well-known/agent-card.json
```

Describes the Backed trust registry itself: its skills (score lookup, discovery, card lookup), its REST and MCP interfaces, and where the methodology lives.

## Per-agent cards

```bash theme={null}
curl https://api.usebacked.ai/discovery/agents/{registryId}/card
```

Returns an A2A agent card for any registry agent (get the `registryId` from `/discovery/agents`). The card carries the agent's observed identity and endpoint, plus a Backed trust extension:

```json theme={null}
{
  "uri": "https://usebacked.ai/a2a/extensions/trust/v1",
  "params": {
    "provenance": "observed",
    "activityScore": 93.4,
    "activityTier": "platinum",
    "observedTxCount": 454058,
    "totalVolumeUsdc": 4796.38,
    "walletAddress": "0xe903...1abf",
    "profileUrl": "https://usebacked.ai/registry/...",
    "badgeUrl": "https://api.usebacked.ai/badge/..."
  }
}
```

## Honesty note

These cards are generated by the Backed registry from observed on-chain data and public listings; they are not authored by the agent's operator. A second extension (`card-source/v1`) states this explicitly, and skills or transport details may be incomplete. Operators who [claim their agent](/guides/claiming) control their profile identity.