JSON Schema Generator — Free Online
Paste or load JSON to instantly generate a JSON Schema with TypeScript types, Zod schemas, C# classes, and SQL DDL. Everything runs in your browser — your data never leaves your device.
What This Tool Does
The JSON Schema Generator analyzes any JSON data you provide and produces a complete JSON Schema describing its structure. JSON Schema is the standard way to define the shape, types, and constraints of JSON data — used for API validation, form generation, documentation, and ensuring data quality in ETL pipelines.
Writing JSON Schema by hand is tedious and error-prone, especially for deeply nested or large JSON structures. This tool infers the schema automatically: it detects types, identifies required fields, recognizes string formats (email, URI, date-time, UUID), handles nullable values, and merges array item schemas intelligently. You can then export the result as TypeScript types, Zod validation schemas, C# POCO classes, or SQL DDL statements.
All processing happens in a Web Worker inside your browser. Your JSON is never transmitted over the network — making this safe for sensitive data like API responses, configuration files, and production database exports.
How to Use the JSON Schema Generator
- Paste your JSON text into the input area, or drag-and-drop a .json file
- Configure inference settings in the options bar: schema draft, required fields, null handling, and more
- The schema generates automatically — or click Generate Schema
- Switch between tabs to view JSON Schema, TypeScript, Zod, C#, or SQL output
- Click Copy or Download to export the output
- Check the Warnings panel for mixed types, empty arrays, or sampling limits
Inference Settings Explained
| Setting | Options | What It Does |
|---|---|---|
| Schema Draft | 2020-12, 2019-09, 07 | Sets the $schema URI and adjusts syntax for the selected JSON Schema draft |
| Required Fields | All / None / Heuristic | "All" marks every observed key as required. "Heuristic" skips nulls, empty strings, and empty collections |
| Null Handling | Nullable / Ignore | "Nullable" adds null to the type union. "Ignore" drops null if another type is observed |
| Array Mode | Union / First / Strict | "Union" merges all item schemas. "First" uses only item[0]. "Strict" warns on mismatches |
| Integer Detection | On / Off | When on, whole numbers become "integer" instead of "number" |
| Format Detection | On / Off | Detects email, URI, date-time, and UUID patterns in strings |
| Additional Properties | true / false | Controls whether unknown properties are allowed in the schema |
💡 Working with JSON data? Use the JSON Formatter to beautify raw JSON first, or the JSON Validator to check for syntax errors. Need to convert formats? Try JSON to CSV or JSON to YAML.
Related Guides & Tutorials
JSON Schema Generator: Complete Guide
How to generate JSON Schema from sample data — inference rules, output formats, and best practices.
TutorialJSON Schema Generator: Step-by-Step Tutorial
Walk through generating a schema from real-world JSON with TypeScript and Zod exports.
Tool{ } JSON Formatter
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Frequently Asked Questions
$schema URI and certain keywords like prefixItems (2020-12) vs items as array (07).type: ["string", "null"]). "Ignore nulls" drops null from the inferred type if a non-null type is also observed for that field.?:. Union types use |. Arrays become T[]. You can also export Zod schemas for runtime validation, C# classes, or SQL DDL.Related Tools
- JSON Formatter — beautify and validate raw JSON before generating a schema
- JSON Validator — check JSON syntax with detailed error messages
- JSON to CSV — flatten JSON arrays into spreadsheet format
- JSON to YAML — convert JSON to YAML configuration format
- JSON to XML — convert JSON to XML for legacy system integrations
- CSV to JSON — convert spreadsheet data to JSON arrays