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Generate JSON Schema Free — Describe Your Data, Get the Schema Instantly

No schema expertise needed. Describe your JSON data structure or paste a sample JSON object, and get a valid JSON Schema ready for API validation and documentation. Free, unlimited, no account required.

plain English in · working code out  ·  ⌘↵ to run

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Live sample · Rename files — type above to make your own
freecodegen.pyPython
import os

# Folder to clean up — change this to your path
FOLDER = "./photos"

for i, name in enumerate(sorted(os.listdir(FOLDER)), start=1):
    src = os.path.join(FOLDER, name)
    if not os.path.isfile(src):
        continue
    ext = os.path.splitext(name)[1].lower()
    dst = os.path.join(FOLDER, f"photo_{i:03d}{ext}")
    os.rename(src, dst)
    print(f"{name} -> {os.path.basename(dst)}")
How it works

This script renames every file in a folder to photo_001, photo_002, and so on, keeping each file’s extension. Set FOLDER to your folder, then run python rename.py from a terminal.

This page generates JSON Schema from plain-English descriptions or from a JSON example you paste in. JSON Schema is a standard way to describe the shape and validation rules of JSON data — essential for API documentation, form validation, data pipelines, and contract testing. If you work with APIs, databases, or configuration files and want to validate that incoming data matches an expected structure, this tool saves you from writing schemas by hand.

How to generate a JSON Schema in seconds

  1. Describe your data structure or paste a JSON sample

    Tell us what fields your JSON object has, what types they are (string, number, boolean, array, object), which ones are required, and any constraints like minimum/maximum values or string formats.

  2. Click Generate

    FreeCodeGen returns a valid JSON Schema document following the JSON Schema Draft-07 or Draft-2020-12 standard. Free, instant, no account.

  3. Read the schema

    Check that each field name, type, and required/optional status matches your actual data. Look at the properties and required arrays in particular.

  4. Copy and use in your project

    Paste the schema into your API documentation (OpenAPI/Swagger), validation library (Ajv, jsonschema, Pydantic), or configuration system. Most tools accept JSON Schema directly.

  5. Test with sample data

    Run your schema through a validator with both valid and invalid JSON samples to make sure it accepts what it should and rejects what it shouldn't.

About this JSON Schema generator

JSON Schema is a vocabulary for describing and validating the structure of JSON data. If JSON is the data, JSON Schema is the contract that says what that data must look like. When your API receives a request body, when your app reads a configuration file, or when a pipeline ingests records from an external source, JSON Schema lets you check automatically that the data has all required fields in the right formats — before any business logic runs.

**What JSON Schema looks like:** Here is a minimal schema for a user object: ```json { "$schema": "https://json-schema.org/draft/2020-12/schema", "type": "object", "properties": { "username": { "type": "string" }, "age": { "type": "integer", "minimum": 0 } }, "required": ["username"] } ```

**Key keywords explained:** - **type**: the data type — "string", "number", "integer", "boolean", "array", "object", or "null". - **properties**: defines the fields of an object. Each field name maps to its own sub-schema. - **required**: an array of field names that must be present. If a field is not in this array, it's optional. - **additionalProperties**: set to false to reject any fields not listed in properties — useful for strict API contracts. - **minimum / maximum**: numeric range constraints. - **minLength / maxLength**: string length constraints. - **pattern**: a regular expression the string must match. - **format**: semantic formats like "email", "date", "uri", "uuid" — validators may or may not enforce these depending on configuration. - **enum**: restrict a field to a specific set of allowed values, e.g. "enum": ["active", "inactive", "pending"]. - **items**: for array fields, describes the schema each item in the array must match. - **$ref**: reference another schema definition to avoid repetition (useful in large schemas).

**Where JSON Schema is used:** - **OpenAPI / Swagger specs:** every request body and response body is defined using JSON Schema. Tools like Swagger UI render these as interactive docs. - **Ajv (JavaScript):** the most popular JSON Schema validator for Node.js and browsers. Validate data in one line: ajv.validate(schema, data). - **Pydantic (Python):** defines data models with validation built in; schemas can be exported as JSON Schema automatically. - **AWS API Gateway, Azure API Management:** can enforce JSON Schema validation on incoming HTTP requests before they reach your backend. - **Configuration files:** tools like VS Code use JSON Schema to provide autocomplete and validation for JSON config files.

**Common mistakes when writing JSON Schema manually:** - Putting field names directly inside the schema root instead of inside "properties". - Forgetting that "required" is an array of strings at the same level as "properties", not inside each property definition. - Using "type": "int" instead of "type": "integer" — the correct types are the full words. - Not testing with invalid data — a schema that only accepts valid input but doesn't reject invalid input is useless for validation.

This generator produces clean, standards-compliant JSON Schema that works with all major validators.

Frequently asked questions

Is this JSON Schema generator free?

Yes — completely free, no signup, no limits. Generate as many schemas as you need.

Which JSON Schema draft does this generate?

By default the generator targets JSON Schema Draft-07, which is supported by nearly all validation libraries. Mention Draft-2019-09 or Draft-2020-12 in your request if you need a newer version.

Can I paste a JSON example and get the schema from it?

Yes. Paste your JSON object in your description and ask for the schema to be inferred from it. The generator will identify field types and suggest which fields should be required.

Will the generated schema work with Ajv, Pydantic, or OpenAPI?

Yes. JSON Schema is a standard, and generated schemas are compatible with Ajv (JavaScript), jsonschema (Python), Pydantic v2 (Python), and OpenAPI 3.x components.

Should I test the schema before using it in production?

Always. Test with both valid data (should pass) and intentionally invalid data (should fail). A schema that doesn't reject bad data provides a false sense of security.

What's the difference between JSON Schema and TypeScript types?

TypeScript types are compile-time checks that disappear at runtime. JSON Schema is a runtime validation standard — it checks actual data values at execution time. They serve different purposes and complement each other.