JSON Schema Generator

From example data to a validation contract

JSON Schema describes what valid JSON looks like: which properties exist, what type each one has and which are required. It is used to validate API requests, document OpenAPI specifications, power form generators and catch bad configuration early. Writing a schema by hand for a large object takes a long time — generating a first draft from real data takes a second.

The generator walks your sample and records the type of every value. For arrays it merges all items: a property is listed as required only if every object contains it, and a property that is sometimes a string and sometimes null gets "type": ["string", "null"]. Strings that all look like dates, date-times, emails, URLs or UUIDs receive a matching format.

How to use it

1. Paste one or more representative JSON documents (wrap several in an array to merge them).
2. Choose the draft version your validator supports — Ajv, Python jsonschema and most modern tools support 2020-12; older tools may need Draft-07.
3. Review the result: add minimum, maxLength, enum or pattern rules where your data has business constraints.

Example

{"id": 7, "email": "a@b.co", "tags": ["x"]}

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Root",
  "type": "object",
  "properties": {
    "id": { "type": "integer" },
    "email": { "type": "string", "format": "email" },
    "tags": { "type": "array", "items": { "type": "string" } }
  },
  "required": ["id", "email", "tags"]
}