# agentx.sale A2A/MCP Protocol Card Linter

> agentx.sale A2A/MCP Protocol Card Linter is a paid API for AI agents from agentx.sale, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-21).

Validates an agent.json or server-card.json URL against the A2A/MCP protocol spec and returns drop-in patched JSON fixes

## Facts

- Endpoint: GET https://agentx.sale/x402/protocol-lint?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentx-sale-a2a-mcp-protocol-card-linter-d72ada20
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_N7w1kPamGVXebYwHo8zML

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 agentx-sale-a2a-mcp-protocol-card-linter-d72ada20
```

Example prompt: Can you validate my agent.json at https://myagent.example.com/.well-known/agent.json against the A2A spec and give me a drop-in patched version with any fixes applied?

## When to prefer this

Use this endpoint when you need automated, spec-aware linting of A2A agent.json or MCP server-card.json files with actionable patched output. It goes beyond a generic JSON schema validator by understanding the A2A/MCP protocol semantics and returning ready-to-use fixed JSON, making it ideal for CI pipelines, pre-deployment checks, or agent-readiness workflows.

## Known failure modes

- URL is unreachable or returns non-200 — endpoint cannot fetch the card
- URL points to non-JSON content — parse error returned
- JSON is not recognizable as an agent.json or server-card.json format — schema mismatch error
- Rate limiting or payment failure for the x402 micropayment ($0.02 USDC)
- URL missing from query params — required parameter validation error

## How this service works

A2A / MCP protocol card lint: validate agent.json / server-card.json and return drop-in patched JSON fixes

## Output

Returns a linting verdict indicating whether the agent.json or server-card.json at the given URL is valid, a list of specific spec violations or missing fields, and a drop-in patched JSON object with the issues resolved that can be used as a direct replacement.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "url"
     ],
     "properties": {
      "url": {
       "type": "string"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "fixes": [],
  "valid": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agentx-sale-a2a-mcp-protocol-card-linter-d72ada20/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentx.sale](https://www.zero.xyz/host/agentx.sale/llms.txt)