JSON → JSON Schema
Infer a JSON Schema from a sample document.
Private by design. Your input never leaves this browser. Conversions run locally on your device.
What this tool handles
- Emits draft-07 or 2020-12.
- Required lists the keys that appear in every observed object.
- additionalProperties can be pinned to false.
- Array items are merged across every element, so a mixed array gets a list of types.
Example
JSON sample
[{"id":1,"name":"Ada"},{"id":2,"name":"Linus"}]JSON Schema
{
"$schema": "http://json-schema.org/draft-07/schema#",
"type": "array",
"items": {
"type": "object",
"properties": {
"id": {
"type": "integer"
},
"name": {
"type": "string"
}
},
"required": [
"id",
"name"
]
}
}When you would use it
- Failing the build when a payload changes — Generate from a recorded request body, commit the schema, and validate against it with ajv or check-jsonschema in a pipeline step so a contract change is caught there instead of in an integration test.
- An entry under components/schemas — OpenAPI 3.1 uses the 2020-12 dialect, so select that draft and delete the $schema line before pasting. For 3.0, a type array such as ["string", "null"] has to be rewritten using nullable.
- Catching typos in a config file — Forbidding additional properties makes an unrecognised key an error rather than something quietly ignored, and it is applied to every object in the document, not only the outermost one.
- Autocomplete while editing JSON by hand — Point an editor at the generated file through a $schema key or a workspace setting and it will complete property names and underline the ones that do not belong.
Common questions
How do I get a required list I can trust?
Feed it an array of records. A key is required when it was present in every object observed at that position, so a single sample makes all of its keys required simply because nothing contradicted them.
Does it infer format, enum or length constraints?
No. Every string is {"type": "string"} with no format, pattern, minLength or enum, and numbers get no minimum or maximum. An email, a UUID and an ISO timestamp are therefore indistinguishable in the output.
How is an array of mixed values typed?
Every element is taken into account, not just the first: [1, "a", null] produces "type": ["integer", "string", "null"], and a position that mixes objects with arrays produces an anyOf that is usually broader than the real contract.
What differs between the two drafts on offer?
Only the $schema URI. The same keywords are emitted either way — no prefixItems, no $defs and no $ref — and every nested schema is written out in place, so a shape repeated twice appears twice.
Related tools
- JSON → TypeScript — Generate TypeScript interfaces or types from a JSON sample.
- JSON → Zod — Generate a Zod schema from a JSON sample.
- JSON → Python — Generate Python dataclasses from a JSON sample.
- JSON → Go — Generate Go structs with json tags from a JSON sample.
- JSON → SQL — Generate a CREATE TABLE statement from flat JSON rows.
- Convert any format — Pick an input format and an output format and convert between any pair.