How do I generate a JSON Schema from sample JSON?

Paste a JSON sample, set a title, pick a draft, and copy the generated schema. Generation runs in your browser. Nested objects and arrays are walked fully, and keys missing across array items are omitted from required.

What is the difference between optional and nullable?

Optional means the key was absent on some array items, so it is not listed in required. Nullable means the key was present and the value was JSON null, so the type includes null (for example type: ["string","null"]). This generator does not collapse them unless the sample showed both.

Which JSON Schema draft should I use?

Draft-07 is still the most widely supported by validators and editors. Use 2020-12 when your tooling explicitly expects that $schema URI. The inferred properties are the same either way.

Why is items or properties empty?

Empty arrays have no elements to inspect, so items is {}. Empty objects have no keys, so properties is empty. Paste a populated example to get concrete types.

Are string formats always correct?

Formats are heuristics from the sample values (email, uri, uuid, date, date-time). Review them before locking a production contract - a string that looks like an email in the sample may not always be one.

No. Schema generation runs only in this tab. The sample never leaves your browser.

How is this different from the JSON to TypeScript converter?

Both walk the same kind of sample. This page emits JSON Schema for validators and OpenAPI drafts. The TypeScript converter emits interfaces or type aliases for application code. Use both from the same payload when you need a contract and typed clients.

Does additionalProperties: false reject unknown keys?

Yes when you leave Reject extras on. That is useful for strict API contracts. Switch to Allow extras if clients may send fields you have not seen in the sample yet.

Developer Tools

JSON Schema Generator

Generate a draft JSON Schema from a JSON sample in your browser - no account, no upload, no CLI.

Try a sample

JSON sample

Generation runs in your browser. The JSON never leaves this device.

Schema title

Becomes the top-level title field in the generated schema.

JSON Schema draft

Draft-07 is the most widely supported. Use 2020-12 when your tooling expects the newer URI.

Additional properties

Reject extras emits additionalProperties: false on objects. Allow extras omits that keyword.

Properties

Required

Optional

Formats

Optional means the key was missing on some array items. Nullable means the sample contained JSON null. format hints come from common string patterns (email, uri, uuid, date, date-time).

Inference notes

The JSON root is an array. The schema validates an array; items describes each element.

$[*].lastLogin was only ever null. Add a real value in the sample to infer the non-null type.

Inferred property report
Path	Type	Flags
$[*].id	integer	required
$[*].name	string	required
$[*].role	string	required
$[*].email	string (email)	optional email
$[*].address	object	required
$[*].address.city	string	required
$[*].address.postcode	string	optional
$[*].lastLogin	null	optional nullable
$[*].tags	array<string>	optional

JSON Schema

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "User",
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "id": {
        "type": "integer"
      },
      "name": {
        "type": "string"
      },
      "role": {
        "type": "string"
      },
      "email": {
        "type": "string",
        "format": "email"
      },
      "address": {
        "type": "object",
        "properties": {
          "city": {
            "type": "string"
          },
          "postcode": {
            "type": "string"
          }
        },
        "required": [
          "city"
        ],
        "additionalProperties": false
      },
      "lastLogin": {
        "type": "null"
      },
      "tags": {
        "type": "array",
        "items": {
          "type": "string"
        }
      }
    },
    "required": [
      "id",
      "name",
      "role",
      "address"
    ],
    "additionalProperties": false
  }
}

About JSON Schema Generator

Generate a draft JSON Schema from a JSON sample in your browser - no account, no upload, no CLI. Paste an API response or, better, an array of records. Nested objects become nested schemas, arrays are typed from every element (not only the first), and identical missing-key patterns become optional (omitted from required). JSON null becomes a nullable type instead of collapsing into optional. String formats are inferred when values look like email, uri, uuid, date, or date-time. Choose Draft-07 or 2020-12, then copy or download the schema. Pair it with the JSON to TypeScript Converter for interfaces from the same sample, or the JSON Minifier if the payload arrived minified.

How to Use JSON Schema Generator

Paste JSON (an array of records infers optional keys more accurately than a single object). Load a sample if you want to see optional vs nullable first.
Set the schema title and pick Draft-07 (default) or 2020-12. Choose whether objects reject or allow additional properties.
Read the inference report: property count, required keys, optional keys, and format hints. Warnings flag empty arrays, empty objects, all-null fields, and mixed unions.
Copy the JSON Schema or download a .schema.json file. Use it in AJV, Zod (via converters), OpenAPI drafts, or CI validators.
Nothing is sent to a server. Invalid JSON reports a line and column.

JSON Schema Generator Examples

Optional key from an array of records

[{"sku":"A1","qty":2},{"sku":"B7","qty":1,"gift":true}] becomes an array schema whose items require sku and qty, while gift is optional (not in required).

Nullable vs optional

Two users where email is missing on one row and note is null on the other emit email as optional string and note as type ["string","null"]. Missing keys and JSON null stay distinct.

String format hints

Values that look like emails, https URLs, UUIDs, ISO dates, or date-times get format: email, uri, uuid, date, or date-time so validators can enforce them.

Empty containers

{"items":[],"meta":{}} types items as an array with empty items schema and meta as an object with no properties. Warnings tell you to paste a richer sample.

Draft-07 vs 2020-12

Both drafts share the same inferred shape. Draft-07 uses the classic $schema URI most tooling still expects. Switch to 2020-12 when your stack documents that dialect.

Common Use Cases

Drafting a JSON Schema before the OpenAPI / AsyncAPI spec exists
Validating webhook payloads (Stripe, GitHub, Slack) in CI with AJV
Turning a fixture file into a contract for contract tests
Bootstrapping schema for config files and feature-flag payloads
Pairing with TypeScript interfaces from the same sample JSON

Frequently Asked Questions about JSON Schema Generator

How do I generate a JSON Schema from sample JSON?: Paste a JSON sample, set a title, pick a draft, and copy the generated schema. Generation runs in your browser. Nested objects and arrays are walked fully, and keys missing across array items are omitted from required.
What is the difference between optional and nullable?: Optional means the key was absent on some array items, so it is not listed in required. Nullable means the key was present and the value was JSON null, so the type includes null (for example type: ["string","null"]). This generator does not collapse them unless the sample showed both.
Which JSON Schema draft should I use?: Draft-07 is still the most widely supported by validators and editors. Use 2020-12 when your tooling explicitly expects that $schema URI. The inferred properties are the same either way.
Why is items or properties empty?: Empty arrays have no elements to inspect, so items is {}. Empty objects have no keys, so properties is empty. Paste a populated example to get concrete types.
Are string formats always correct?: Formats are heuristics from the sample values (email, uri, uuid, date, date-time). Review them before locking a production contract - a string that looks like an email in the sample may not always be one.
Is my JSON uploaded?: No. Schema generation runs only in this tab. The sample never leaves your browser.
How is this different from the JSON to TypeScript converter?: Both walk the same kind of sample. This page emits JSON Schema for validators and OpenAPI drafts. The TypeScript converter emits interfaces or type aliases for application code. Use both from the same payload when you need a contract and typed clients.
Does additionalProperties: false reject unknown keys?: Yes when you leave Reject extras on. That is useful for strict API contracts. Switch to Allow extras if clients may send fields you have not seen in the sample yet.

JSON to TypeScript Interface Converter

Free JSON to TypeScript interface converter. Paste a JSON sample, generate nested interfaces or type aliases, and keep optional keys separate from JSON null. Nothing is uploaded.

JSON Minifier & Formatter

Free online JSON minifier and formatter. Minify JSON to shrink payloads or beautify (pretty-print) JSON with 2-space indentation. Validates as you go - no upload required.

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Test JSONPath online in your browser. Extract a field from JSON, try a filter example, and copy normalized paths - nothing is uploaded.

JSON Diff Checker

Free structural JSON diff in your browser. Compare two JSON documents by keys and values - not line order. Nothing is uploaded.