What is JSON Schema?

JSON Schema is a vocabulary for annotating and validating JSON data. A schema document describes the expected structure of a JSON value: which keys are required, what types are allowed, and how nested objects and arrays are shaped.

It is supported by validators in every major language (Ajv for JavaScript, jsonschema for Python, networknt for Go) and used in OpenAPI specs, VS Code settings, GitHub Actions, and many API platforms. Draft-07 is the most widely supported version; Draft 2020-12 is the latest stable specification.

How the inference works

The generator traverses your JSON recursively. Arrays are typed by their elements: if all items share the same structure, a single schema is inferred; mixed arrays produce {"oneOf":[...]}.

string{"type":"string"}

integer{"type":"integer"}

float{"type":"number"}

boolean{"type":"boolean"}

null{"type":"null"}

object{"type":"object","properties":{...}} + required[]

After generation: refine and validate

The generated schema is a structural starting point. To validate your JSON against it, paste both into an online validator or use a library like Ajv (npm install ajv). For API schemas, consider generating from your OpenAPI spec with tools like openapi-typescript rather than from example JSON.

minLengthmaxLength — bounds for strings

minimummaximum — bounds for numbers

patternregex-validated strings

formatemails, dates, and other known shapes

enumfixed set of allowed values

additionalPropertiesfalse — reject unknown keys

JSON → Schema

What is JSON Schema?

How the inference works

After generation: refine and validate