SchemaCheck Agent

A machine-native paid API for validating JSON payloads against JSON Schema.

Live endpoint: https://projectx402-production.up.railway.app
MCP endpoint: https://projectx402-production.up.railway.app/mcp

What it does

Send a JSON Schema and a JSON payload. Get back a structured validation result: whether the payload is valid, a list of errors with JSONPath locations, a plain-English summary, and optionally a suggested corrected payload.

Built for autonomous agents, backend pipelines, and developers who need reliable, cheap, per-call JSON validation without managing a library dependency.

Supports two access modes:

• MCP tools via Streamable HTTP — connect any MCP-compatible client directly, fiat billing via MCP-Hive
• REST + x402 — HTTP endpoint with USDC micropayment on Base mainnet ($0.005/call)

Endpoints

Quickstart — MCP (recommended for AI agents)

Add to your MCP client config:

{
  "mcpServers": {
    "schemacheck": {
      "url": "https://projectx402-production.up.railway.app/mcp"
    }
  }
}

Two tools are available: validate_schema (full, with repair) and validate_schema_trial (free, no repair). See docs/agent_quickstart.md for a full Python MCP client example.

Quickstart — trial (no payment)

curl -X POST https://projectx402-production.up.railway.app/v1/schema-check/trial \
  -H "Content-Type: application/json" \
  -d '{
    "json_schema": {
      "type": "object",
      "required": ["name", "email"],
      "properties": {
        "name": {"type": "string"},
        "email": {"type": "string", "format": "email"}
      },
      "additionalProperties": false
    },
    "payload": {
      "name": "Ada Lovelace",
      "email": "not-an-email"
    }
  }'

Response:

{
  "valid": false,
  "errors": [
    {
      "path": "/email",
      "code": "format",
      "message": "'not-an-email' is not a valid email address.",
      "schema_path": "/properties/email/format"
    }
  ],
  "summary": "The payload failed validation. 1 error found.",
  "suggested_payload": null,
  "confidence": 0.9,
  "meta": {
    "strictness": "normal",
    "repair_attempted": false,
    "engine": "jsonschema",
    "schema_draft": "auto"
  }
}

Quickstart — paid endpoint (x402)

The paid endpoint requires an x402 v2 USDC micropayment of $0.005 per call on Base mainnet.

Payment flow:

1. Send request to POST /v1/schema-check without payment headers.
2. Receive 402 Payment Required with x402Version=2 and payment details.
3. Sign and send payment via PAYMENT-SIGNATURE header.
4. Receive 200 with validation result.

See docs/agent_quickstart.md for a full Python example with x402 payment handling.

Request fields

Response fields

Error codes

required · type · format · enum · additionalProperties · minimum · maximum · minLength · maxLength · pattern · items · oneOf · anyOf · allOf · unknown

Pricing

Payment is handled via the x402 protocol — an HTTP-native micropayment standard using USDC on Base.

Health check

curl https://projectx402-production.up.railway.app/health

{"status": "ok", "service": "schemacheck-agent", "version": "0.3.0"}

Reporting issues

If you encounter unexpected responses, payment errors, or validation bugs, please open a GitHub issue.

Include:

• The endpoint called (/v1/schema-check or /v1/schema-check/trial)
• The request body (redact any sensitive data)
• The response received
• The X-Request-ID header value from the response if available

Further reading

• docs/agent_quickstart.md — Full integration guide: MCP tools, x402 payment, trial endpoint
• api_contract.md — Full API contract and error shape reference
• docs/x402_real_flow.md — x402 v2 payment flow details