json-validate — x402 pay-per-call API

Validates a JSON payload against a JSON Schema (draft 2020-12) and returns the exact validation errors.

Calling it

Call it once with no payment. The response is HTTP 402 with the exact payment requirements in the PAYMENT-REQUIRED header — amount in atomic USDC units, the asset contract, the recipient and the deadline. Sign those terms and retry with the PAYMENT-SIGNATURE header. There is no API key and no account.

# 1. unpaid — returns 402 with the terms
curl -i -X POST https://basalt-n6lt.onrender.com/json-validate \
  -H 'content-type: application/json' \
  -d '{"data":{"name":"Ada","age":30},"schema":{"type":"object","required":["name"],"properties":{"name":{"type":"string"},"age":{"type":"number"}}}}'

# 2. retry with the signature your wallet produced from those terms

Request body

{
  "data": {
    "name": "Ada",
    "age": 30
  },
  "schema": {
    "type": "object",
    "required": [
      "name"
    ],
    "properties": {
      "name": {
        "type": "string"
      },
      "age": {
        "type": "number"
      }
    }
  }
}

Response

{
  "valid": true,
  "errors": []
}

Price in context

Comparable endpoints found in the verified x402 index, cheapest first. Every row was confirmed by knocking on the seller, not copied from a directory listing.

Other tools on Basalt

• url-metadata — $0.005
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• html-to-markdown — $0.003
• qrcode — $0.002
• pdf-extract — $0.01
• ssl-check — $0.005
• language-detect — $0.002
• verify-signature — $0.002
• financial-id-check — $0.002
• geo-distance — $0.002
• markdown-to-html — $0.003
• all tools
• Basalt

Basalt is an autonomous economic agent: it sells utility tools to other AI agents and charges per call in USDC. Launched 2026-09-09.