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Agent402 JSON Schema Validator
x402
Agent402 JSON Schema Validator is a paid API for AI agents from agent402.co.uk, paid per call via x402, $0.001/call, status down (last checked 2026-09-14).
Validates a JSON instance against a JSON Schema (type, required, properties, enum, min/max) and returns a deterministic pass/fail result with errors
Price / call$0.001
Success—
StatusDown
How this service works
Don't burn tokens on deterministic work. Go/no-go jobs first: payout preflight, text firewall (PII/secrets), budget check — then rails, calendars, finmath. x402 USDC on Base. UK + global. agent402.co.uk — not agent402.tools. $0.001–$0.002 USDC on Base. No API keys.
Output
Returns a JSON object with a boolean 'valid' field (true/false) and an 'errors' array listing any schema violations with details about which constraint failed (type mismatch, missing required field, enum violation, min/max breach, etc.). On success with no errors, 'errors' is an empty array.
Example use cases
Guard LLM output before database write
“I need you to validate this JSON object my LLM just generated against the schema before we write it to the database — schema requires 'userId' (string, required), 'amount' (number, min 0, max 10000), and 'currency' (enum: USD, GBP, EUR). Here's the instance: {"userId": "abc123", "amount": -50, "currency": "USD"}.”
Verify agent tool output structure
“The agent tool returned this JSON — can you check it against the required schema (must have 'action' as a string, 'payload' as an object, and 'timestamp' as a string, all required) and tell me exactly which fields are missing or wrong?”
Catch enum violations in structured output
“My LLM produced this JSON for a booking request and I want to catch any schema errors before it triggers a payment — schema says 'status' must be one of pending/confirmed/cancelled and 'seats' must be an integer between 1 and 10. Validate this instance: {"status": "approved", "seats": 0}.”
Technical details
Endpoint
POSThttps://agent402.co.uk/v1/validate/json-schemaWhen to prefer
Choose this endpoint when you need fast, deterministic, server-side JSON Schema validation — particularly to catch LLM structured-output errors before they trigger irreversible side effects like payments or database writes. Prefer it over rolling your own validation logic when your agent is already calling micro-APIs and you want a cheap ($0.001), stateless, no-key-required validation step in a pipeline. Best for the core subset of JSON Schema (type, required, properties, enum, min/max). If you need full JSON Schema draft support including $ref or complex combiners, consider a dedicated validation library instead.
Side effects
- Malformed JSON schema object causes 400-level error
- Instance or schema field missing from request body returns error
- Schema features outside the deterministic subset (e.g. $ref, allOf, oneOf) may not be supported
- Network or payment (x402) failure returns no validation result
- Very deeply nested schemas may exceed processing limits
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| schema | object | JSON Schema subset |
| instance | object | Value to validate |
Output
Schema · Response
{
"type": "json",
"example": {
"valid": true,
"errors": []
}
}Tags
x402
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