# Council of AI — A2A Agent Population Slice

> Council of AI — A2A Agent Population Slice is a paid API for AI agents from councilof.ai, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-02).

Returns a signed, attestation-backed population slice of distinct AI agents indexed in the A2A (Agent-to-Agent) registry frame, with cryptographic evidence for verification.

## Facts

- Endpoint: GET https://councilof.ai/api/pop/a2a?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/council-of-ai-a2a-agent-population-slice-4facb269
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_FLpXnBt1LPlCH2fN8kL-G

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability council-of-ai-a2a-agent-population-slice-4facb269
```

Example prompt: Pull the latest signed population slice from Council of AI for the A2A agent registry — I want to see how many distinct agents are indexed and check the ed25519 attestation signature.

## When to prefer this

Choose this endpoint when you need a cryptographically signed, independently verifiable snapshot of the A2A agent population with checkable evidence — particularly for governance audits, compliance reporting, or cross-verification of agent registry claims. Prefer this over raw registry scrapes when attestation and tamper-evidence matter. Not suitable for real-time streaming or querying individual agent details.

## Known failure modes

- Payment not included or invalid: returns HTTP 402 requiring x402 USDC payment
- Invalid method (POST, PUT, etc.): schema only accepts GET, HEAD, DELETE
- Data not yet indexed: state field may reflect non-INDEXED status
- Attestation signature null: unsigned supporting runs are labelled as such, not a hard error
- Network or provider downtime: standard HTTP 5xx response

## How this service works

We measure how AI systems behave against frozen, published tests and publish checkable evidence. Issued measurement cards are signed; unsigned supporting runs are labelled. Read the live board and corrections ledger.

## Output

A JSON object containing: the count of distinct agents (n), slice ID (a2a), kind label (slice), raw population rows/artifact bytes, an as_of timestamp, indexing state, unit description clarifying this is one frame (not a global count), schema version, settlement metadata (payer, network, transaction), source file paths, and a full attestation block with ed25519 signature, SHA-256 of rows, surface label, and card schema URL. The signature field may be null for unsigned supporting runs.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "n": 391,
  "id": "a2a",
  "kind": "slice",
  "rows": "<the population rows / artifact bytes, verbatim>",
  "as_of": "2026-09-17T05:48:05Z",
  "state": "INDEXED",
  "n_unit": "distinct agents in the a2aregistry-org frame (one frame; not a global count)",
  "schema": "csoai.population-door/0.1",
  "settle": {
   "payer": "<0x… or null>",
   "network": "<caip2 or null>",
   "transaction": "<0x… or null>"
  },
  "source": [
   "/interop/agent-population-2026-09-17.json",
   "/interop/a2a-directories.json"
  ],
  "attestation": {
   "schema": "https://councilof.ai/schema/card-v0.json",
   "sha256": "<hex>",
   "payload": {
    "kind": "csoai.population.slice/0.1",
    "rows_sha256": "<hex>"
   },
   "surface": "population.slice",
   "sig_ed25519": "<hex or null>"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/council-of-ai-a2a-agent-population-slice-4facb269/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from councilof.ai](https://www.zero.xyz/host/councilof.ai/llms.txt)