Visual JSON Schema Builder
Build a JSON Schema from scratch — add properties, pick types, set constraints. No sample JSON needed.
Sometimes you're not validating data you already have — you're designing a contract before any data exists. This builder skips the sample-JSON step entirely: add a property, pick its type from a dropdown, set constraints, and the JSON Schema on the right updates live. Nest objects and arrays as deep as you need.
- ✓No sample JSON required — build the shape you want directly
- ✓Every core type with its relevant constraints exposed as fields
- ✓Nested objects and arrays, arbitrarily deep
- ✓required, description, enum, pattern, format — all visual
- ✓Draft 2020-12 output, ready to paste into your validator or API docs
Builder vs. Generator — Two Different Starting Points
JSON Schema Generatorworks backwards from data you already have — paste a JSON sample and it infers a schema from what's there. This tool works forwards: you design the schema first, often before any real data exists yet, which is the more natural starting point when you're specifying an API contract or a config format from scratch rather than reverse-engineering one.
| JSON Schema Generator | Visual JSON Schema Builder | |
|---|---|---|
| Starting point | An existing JSON sample | Nothing — you design it |
| Best for | Documenting data you already have | Specifying a contract before data exists |
| Types are | Inferred from example values | Chosen explicitly per property |
| Constraints | Not inferred (values only suggest type) | Set directly — min/max, pattern, enum, format |
Using the Output
The generated schema is standard Draft 2020-12 JSON Schema — paste it straight into JSON Schema Validator to test it against real payloads, use it with ajv or zod-to-json-schema's inverse in a Node.js validation layer, or drop it into OpenAPI/Swagger docs as a component schema. Every object gets additionalProperties: false by default, so unexpected fields are rejected rather than silently allowed — remove that line manually if you want a looser contract.
Common Uses
- ▸Specifying an API contract up front — Design the request/response shape before any backend code exists, so frontend and backend teams build against the same agreed contract.
- ▸Dynamic forms and admin panels — Many form-rendering libraries and admin-panel generators consume a JSON Schema directly to render inputs — build the schema visually instead of hand-writing the JSON.
- ▸Config file specification — Define the exact shape and constraints of an app's config file before writing any parsing or validation code.
- ▸Rapid prototyping — Sketch out a data model visually during a design discussion, without needing sample data or writing raw JSON Schema syntax on the spot.