JSON Schema Generator
Generate a draft 2020-12 JSON Schema from any JSON object — entirely in your browser. Your payloads never leave the page.
- Runs in your browser
- No upload, no tracking
- Free forever
How it works
A JSON Schema generator infers a formal JSON Schema from an example JSON object — describing each field's type, which keys are required, and how nested objects and arrays are shaped — so you can validate future payloads against a contract. This tool emits a draft 2020-12 schema and runs entirely client-side, so sample data never leaves your machine. It is built by JusDB, a managed database operations team, for the schema work that surrounds every API and data store.
- 1
Paste an example object
Drop a representative JSON object into the input panel, or click Sample to load one. Use the most complete record you have so every field is inferred.
- 2
Name the schema
Set a Schema title — it becomes the title keyword in the output so the schema is self-describing.
- 3
Read the inferred schema
The right panel shows a draft 2020-12 schema with type, properties, required and additionalProperties: false, generated live as you type.
- 4
Copy and refine
Copy the schema with one click, then loosen additionalProperties or required by hand wherever your data is optional or open-ended.
Frequently asked questions
- Is my JSON sent to a server?
- No. The schema is inferred locally in your browser with JavaScript. Your JSON is never uploaded to JusDB or any server.
- Which JSON Schema draft is produced?
- It emits a draft 2020-12 schema, declared with the $schema keyword, including type, properties, required and additionalProperties: false.
- How are required fields determined?
- Every key whose value is not null in your sample JSON is added to the required array. Keys with null values are treated as optional.
- Does it handle nested objects and arrays?
- Yes. Nested objects become nested schema definitions and arrays infer their items schema from the first element. Inference is capped at a safe depth to avoid runaway recursion.
- Can I set a title for the schema?
- Yes. The schema title field lets you name the generated schema, which is emitted as the title keyword. Click Sample to load an example object, and Clear to reset the input.
- Is the generated schema strict?
- It sets additionalProperties: false on each object, so any key not present in your sample is rejected by a validator. Loosen this manually if your data has optional or open-ended properties.
Getting the most out of JSON Schema
JSON Schema is a vocabulary for describing the shape of JSON data so a machine can validate it. Teams reach for it to guard API request and response payloads, to lint configuration files before they ship, to drive UI form generation, and to power code generation that produces typed models in TypeScript, Go, or Python. Because the schema is just JSON, it doubles as living documentation of the contract between a producer and every consumer downstream.
Inference is a starting point, not the finished schema
A sample object can only tell the generator what one record happened to contain. It cannot know that an email string must match an email format, that status is really an enum of three allowed values, that quantity must be a positive integer, or that a field present in your example is actually optional. Treat the generated output as scaffolding: add required deliberately, tighten numeric and string constraints with minimum, maxLength and pattern, and replace inferred free-text fields with enum or format wherever the domain is fixed.
A clean, indented sample makes the inference easier to read and correct. If your example is minified or messy, run it through the JSON formatter first so structural problems are obvious before you generate a schema from it.
Draft versions and the OpenAPI connection
This tool emits draft 2020-12, the current revision, which uses $schema to declare its dialect and supports prefixItems for tuple-style arrays. Plenty of validators in the wild still target draft-07, so confirm what your tooling expects before adopting newer keywords. OpenAPI is closely related but not identical: OpenAPI 3.1 aligns with JSON Schema 2020-12, while 3.0 uses an older, slightly divergent subset, so a schema that validates standalone may need small adjustments to drop cleanly into a components/schemas block.
Validating data before it reaches a database
Schema validation is cheapest at the edge. Running an incoming payload against a schema in your API layer rejects malformed input long before it becomes a failed insert, a constraint violation, or a corrupt row that someone has to clean up later. The schema and your table definition should agree: a non-null column maps to a required property, a varchar(120) maps to maxLength: 120, and a check constraint maps to a numeric or pattern rule. If you are designing that storage layer, the team behind these tools at JusDB managed databases works on exactly this boundary between application contracts and the data store.
Keep schemas in version control next to the code they describe and validate them in CI. When the contract changes, the diff on the schema file becomes a clear, reviewable record of what consumers need to adapt to — far more reliable than tracking shape changes by reading endpoint handlers.