# Council of AI — AI Marking Evidence Checker (art50)

> Council of AI — AI Marking Evidence Checker (art50) is a paid API for AI agents from councilof.ai, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-13).

Checks a given URL for AI content marking evidence (e.g. C2PA manifests) and returns a signed verification card with detection results

## Facts

- Endpoint: GET https://councilof.ai/api/art50/marking-evidence
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/council-of-ai-ai-marking-evidence-checker-art50-ffd0380b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_gIQocSF8dmBQZjEB5hx_S

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-ai-marking-evidence-checker-art50-ffd0380b
```

Example prompt: Can you check whether this image at https://example.com/photo.jpg has any AI content marking or C2PA provenance data attached to it, and give me the signed verification result?

## When to prefer this

Use this endpoint when you need to programmatically verify whether a specific URL's content carries AI provenance marking (C2PA, SynthID, etc.) and want a cryptographically signed, structured evidence card backed by the GSPC Art50 standard. Prefer this over generic C2PA tools when you need a signed, auditable record from a neutral third-party council, or when integrating with GSPC-compatible workflows.

## Known failure modes

- Invalid or unreachable URL returns an error or empty result
- URL scheme other than HTTPS is rejected by schema validation
- Content type at URL is unsupported for marking detection
- Payment not completed (x402 payment required) — returns 402 before processing
- Signature field may be null if signing is unavailable
- Some marking methods (e.g. SynthID, root_inclusion) are always listed as unmeasured if not supported

## How this service works

Explore the current GSPC measurements, see the published change record, verify signed evidence, and access the supported public feeds.

## Output

A signed JSON card (CSOAI schema card-v0) containing: the kind identifier (csoai.art50.marking-evidence/0.1), an array of checked methods with their results (e.g. c2pa.manifest-store: NOT_DETECTED), human-readable statements summarizing the findings, a list of unmeasured methods (e.g. root_inclusion, watermark.synthid), the surface name (art50.marking-evidence), and an ed25519 signature (hex or null) for cryptographic verification.

## 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"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "url"
     ],
     "properties": {
      "url": {
       "type": "string",
       "format": "uri",
       "description": "HTTPS URL of the output to measure"
      },
      "preview": {
       "type": "string",
       "const": "1"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "schema": "csoai.art50.marking-evidence/0.1",
  "measurement": {
   "checked": []
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/council-of-ai-ai-marking-evidence-checker-art50-ffd0380b/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)