# fastapi.online — JSON Schema Generator

> fastapi.online — JSON Schema Generator is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-18).

Generates a JSON Schema definition from a provided JSON example or description string

## Facts

- Endpoint: POST https://api.fastapi.online/json-schema-generate?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-18
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastapi-online-json-schema-generator-4cb853cb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_yT_UduC8krskhD8WvXiD1

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 fastapi-online-json-schema-generator-4cb853cb -d '<json body>'
```

Example prompt: Can you generate a JSON Schema from this JSON example I have: {"name": "Alice", "age": 30, "email": "alice@example.com", "active": true}?

## When to prefer this

Choose this endpoint when you need to programmatically derive a JSON Schema from an existing JSON example without manual schema authoring. It is ideal for developer automation workflows, API documentation generation, data validation setup, or when onboarding unfamiliar data structures. At $0.001 USDC per call with no signup required, it suits lightweight, pay-as-you-go agent pipelines that need schema generation as a utility step.

## Known failure modes

- Empty or missing 'json' field returns a validation error
- Malformed or non-JSON string input may result in a parse error or unexpected schema
- Input exceeding 20,000 characters is rejected due to maxLength constraint
- Ambiguous or deeply nested JSON may produce an overly generic schema with 'any' types
- Payment failure via x402 protocol results in 402 response and no schema returned

## How this service works

Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&amp;A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding &amp; crypto utilities, date/time calculators, geo/coordinate math, math &amp; 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 Schema document (typically a JSON object conforming to the JSON Schema specification) inferred from the provided JSON input, including type definitions, required fields, and property structures.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "json": {
   "type": "string",
   "maxLength": 20000,
   "minLength": 1
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastapi-online-json-schema-generator-4cb853cb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.fastapi.online](https://www.zero.xyz/host/api.fastapi.online/llms.txt)