JSON Schema Builder & Validator
Paste a JSON sample to infer its schema automatically. Then validate any JSON against that contract — with human-readable errors.
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Create a contract from sample JSON and verify whether other payloads match it.
What to expectPaste a sample to infer schema automatically, review or edit the schema, then validate any JSON against it with readable errors.
Good to knowInferred schemas are a fast starting point, but you may still want to tighten required fields and constraints manually.
How it works
- Paste a representative JSON sample into the left panel to infer an initial schema.
- Review and optionally edit the generated JSON Schema in the center panel to match your contract.
- Paste additional JSON into the right panel to validate it against the schema and inspect any field-level errors.
All inference and validation happen entirely in your browser. Sample data and schemas are never uploaded or stored on a server.
Sample JSON
Paste a representative JSON sample. The schema will be inferred automatically.
OPTIONS
Schema
Review or edit the inferred JSON Schema. Editing disables auto-inference until reset.
Validate JSON
Paste any JSON here to validate it against the schema.
Validation results appear here
Add a schema and JSON input to validate the payload.
Frequently Asked Questions
What is the difference between JSON Schema Draft 7 and Draft 2020-12?
Draft 2020-12 adds improved vocabularies, $dynamicRef, and other features on top of Draft 7. The builder focuses on the widely used subset of keywords so that schemas you infer here work well with mainstream validators such as AJV.
Can I infer a JSON Schema from my existing JSON data?
Yes. Paste one or more representative JSON samples into the left panel and the tool will infer types, required properties, and nested objects. You can then refine the generated schema in the center panel before using it in your API or validation layer.
Is the inferred schema guaranteed to match every payload my API will receive?
No inference engine can predict unseen edge cases. The schema here is based solely on the samples you provide, so you should treat it as a starting point and explicitly tighten or relax rules to reflect your real contract, especially around required fields and enums.
Can I validate JSON payloads against a schema from another system?
Yes. You can paste any existing JSON Schema into the schema panel and use the right-hand validator panel to check payloads against it. This is handy for debugging third-party webhooks or documenting integration contracts.
Does validation happen locally or on a server?
Both schema inference and validation run entirely in your browser using a client-side validator. Sample payloads and schemas are never uploaded or stored remotely, which makes it safe to paste production-like examples during development.
How to use this tool
Left panel: paste a JSON sample and the schema is inferred automatically. Center panel: review or edit the schema. Right panel: paste any JSON to validate it against the schema. Errors show exactly which field failed and why.