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fastapi.online — JSON Schema Validation
x402
fastapi.online — JSON Schema Validation is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.0005/call, status down (last checked 2026-10-22).
Validates a JSON string against a provided JSON Schema and returns whether it is valid
Price / call$0.0005
Success—
StatusDown
How this service works
Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding & crypto utilities, date/time calculators, geo/coordinate math, math & finance calculators, novelty tools, and business/social writing generators — 179 endpoints in all, across multiple specialized self-hosted models. Pay per call with crypto — no signup — or get an API key.
Output
Returns a JSON object with a 'valid' boolean field indicating whether the provided data string conforms to the given schema. May include additional fields describing validation errors or details when invalid.
Example use cases
API payload pre-flight check
“Before I send this JSON payload to the orders API, validate it against this schema to make sure it won't be rejected: data is '{"orderId":"abc123","quantity":2}' and the schema requires orderId as a string and quantity as an integer.”
Config file format enforcement
“Check whether this config JSON string '{"timeout":30,"retries":"three"}' is valid against my schema that requires both fields to be integers — I suspect there's a type error.”
User-submitted form data verification
“A user just filled out a registration form and the output is this JSON: '{"email":"user@example.com","age":25}' — can you validate it against my schema that requires email as a string and age as a number before I save it?”
Technical details
Endpoint
POSThttps://api.fastapi.online/validate-json?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a quick, lightweight, pay-per-call JSON Schema validation without signup. Ideal for agents that occasionally need to validate JSON payloads against schemas without provisioning a dedicated validation service. Avoid if you need deeply nested $ref resolution or complex JSON Schema draft versions beyond what the service supports.
Side effects
- Malformed JSON data string causes parsing error
- Invalid or unparseable schema object returns error
- Missing required 'data' or 'schema' fields returns 400
- Schema references unsupported JSON Schema features and validation fails unexpectedly
- Payment not processed (402) if no API key and crypto payment fails
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| data | — | |
| schema | object |
Tags
x402
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