JSON Schema Generator
Infer a JSON Schema (draft 2020-12) from a JSON sample
Ideal for LLM structured output (OpenAI/Anthropic tool calling), API validation with ajv, or documenting a payload. All fields in the sample are marked required — remove any that are optional.
How it works
- 1Paste a JSON sample
Drop a representative object or array — an API response, a config, an LLM function call payload.
- 2Name the root type
Give the schema a title (defaults to 'RootSchema'). Used by generators and error messages.
- 3Copy the schema
Paste directly into your LLM tool definition, ajv, or API docs.
About JSON Schema Generator
Free online JSON Schema generator. Paste a JSON sample to instantly get a draft-2020-12 JSON Schema with types, required fields, and nested object/array shapes. Ideal for LLM structured output (OpenAI/Anthropic tool calling), ajv validation, and API contracts. JSON Schema Generator on 712 Tools runs entirely inside your browser using modern JavaScript APIs — no server ever sees your data. That means instant results, complete privacy, and no upload limits.
Whether you need to infer a json schema (draft 2020-12) from a json sample for a debugging session, a quick sanity check, or a production incident, this tool is free to use as many times as you need. There are no watermarks, no sign-up, and no ads inside the tool itself.
Frequently asked questions
Which JSON Schema draft?
Draft 2020-12 — the current version, and what OpenAI and Anthropic expect for structured output / tool calling.
Are all fields marked required?
Yes — every field in your sample. Remove the ones that are conditional from the required array by hand.
How are arrays typed?
The tool merges all items and produces one items schema. Mixed arrays become a union of types.
Is my JSON sent anywhere?
No. Inference happens entirely in your browser.
Read more
LLM token counting and API cost estimation: a 2026 developer's guide
Tokens aren't words, GPT-4o and Claude count them differently, and a 1M-context prompt can cost $30. Here's how tokens actually work, and how to estimate cost before you ship.
JSON Schema for LLM structured output: the developer's shortcut
OpenAI's structured output and Anthropic's tool use both want JSON Schema. Here's the draft that works everywhere, the fields models care about, and how to write one from an example in 10 seconds.
Related tools
JSON to CSV
Convert JSON arrays to downloadable CSV
Timestamp Converter
Convert between Unix time, ISO 8601, and human-readable dates
Markdown to HTML
Convert Markdown to clean HTML with live preview
YAML ↔ JSON
Convert YAML to JSON and back with full syntax validation
JSON → TypeScript
Generate TypeScript interfaces or types from a JSON sample
Base Converter
Convert between binary, octal, decimal, and hexadecimal