JSON to JSON Schema

About this tool

JSON to JSON Schema infers a practical JSON Schema from one pasted JSON example or from an array of examples. It is useful when you have sample API responses, config objects, event payloads, or webhook fixtures and want a starting schema without writing every property by hand.

• Objects and arrays are inferred recursively: nested objects become properties, arrays become items, and arrays with several objects merge the observed item shapes.
• Required keys are data-driven: keys present in every merged object are listed under required; keys missing in some examples become optional.
• Mixed values become unions: for example [1, "two"] produces an item type that accepts both integer and string.
• String formats are detected when enabled: email, URI, date-time, date, UUID (Draft 2020-12), and IPv4.
• Strict by default: additionalProperties: false is emitted unless you turn on “Allow extra properties”.

Everything runs locally in your browser through WebAssembly. Your sample JSON is not uploaded.

Worked example

Input:

[{ "id": 1, "email": "[email protected]" }, { "id": 2, "email": "[email protected]", "admin": true }]

Output excerpt:

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

Limits & edge cases

• This is inference, not proof. A small sample may miss optional fields, allowed enum values, minimums, maximums, string lengths, or domain-specific rules.
• Empty arrays infer items: {} because there are no elements to learn from.
• Incompatible shapes (for example sometimes an object and sometimes a string) are intentionally widened rather than guessed narrowly.
• It does not validate future JSON against the schema; use the generated schema in your validator of choice.

FAQ