# Agent Card Well-Known Linter

> Agent Card Well-Known Linter is a paid API for AI agents from agent-card-validator-mcp.mtree.workers.dev, paid per call via x402, $0.03/call, status unknown (last checked 2026-09-13).

Lints and validates well-known agent card URLs, checking them for correctness and returning provenance-annotated JSON results.

## Facts

- Endpoint: POST https://agent-card-validator-mcp.mtree.workers.dev/v1/wellknowns/lint
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-card-well-known-linter-270c7c12
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_lzJVBxU0PdS90T_a8blvu

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 agent-card-well-known-linter-270c7c12 -d '<json body>'
```

Example prompt: Can you lint and validate the well-known agent card at https://myagent.example.com/.well-known/agent.json and tell me if there are any errors or provenance issues?

## When to prefer this

Use this endpoint when you need to validate or lint an AI agent's well-known card endpoint, particularly in autonomous agent pipelines that need to verify agent card compliance before interacting with another agent. Prefer this over manual inspection when you need structured, provenance-tagged lint results.

## Known failure modes

- Invalid or unreachable well-known URL returns error response
- Malformed agent card JSON causes parse errors in output
- Payment not included or insufficient (x402 payment required at $0.03 USDC)
- URL does not resolve to a valid well-known endpoint
- Network timeout reaching the target well-known URL

## How this service works

Paid agent card and well-known validator route for autonomous agents. Returns JSON with provenance, route-specific evidence, and machine-readable fields. Price 0.03 USDC on Base via x402. Demo/preview: https://agent-card-validator-mcp.mtree.workers.dev/demo/lint. Contact: https://agent-card-validator-mcp.mtree.workers.dev/contact.

## Output

A JSON object containing lint results for the submitted well-known agent card URL, including validation errors, warnings, and provenance metadata about the agent card's structure and compliance.

## Example request

```json
{
 "input": {
  "body": {
   "base_url": "https://example.com"
  },
  "type": "http",
  "method": "POST",
  "bodyType": "json"
 }
}
```

## 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",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "properties": {
      "base_url": {
       "type": "string"
      }
     },
     "additionalProperties": true
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-card-well-known-linter-270c7c12/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent-card-validator-mcp.mtree.workers.dev](https://www.zero.xyz/host/agent-card-validator-mcp.mtree.workers.dev/llms.txt)