About this converter
This free tool converts JSON into Joi. Plain JSON document or sample payload. Joi (Hapi) JavaScript validation schema. The conversion runs entirely client-side: your input is not uploaded or logged. Useful when you want to skip writing types by hand for an API response, a database row, or a config payload.
Why convert JSON to Joi
- • Validate Express / Hapi / Koa request bodies before they hit handlers.
- • Centralize validation rules so endpoints stay consistent.
- • Reject malformed payloads with structured error messages.
How to use
- Paste your JSON on the left panel, or pick one of the sample tabs above.
- The converter infers field names, optionality, and types automatically.
- Copy the generated Joi on the right and drop it straight into your codebase.
Common pitfalls
- • Inferred types only see the payload you pasted. Add nullable / optional flags for fields that can be missing.
- • Numeric types are inferred as integer or float based on the sample. Real APIs sometimes return both — widen to a number/float type when in doubt.
- • Empty arrays default to an `unknown` element type. Paste a non-empty sample to get a meaningful element type.
FAQ
Is this json to joi converter free?
Yes. It is fully free, no signup, and runs entirely in your browser. We do not store your input.
Does it work with nested objects and arrays?
Yes. Nested objects produce separate named types, and arrays infer the element type from the first non-null sample.
What about optional / nullable fields?
Fields whose value is null in the sample (or marked optional in JSON Schema / Prisma / GraphQL) are marked optional/nullable in the output. For real APIs, you may want to widen optionality manually after generation.
Can I generate Joi from multiple JSON samples?
Today the tool processes a single sample. For more aggressive inference across multiple shapes, run the converter on the union/merge of your samples or open an issue.
Is the source code available?
Yes — the entire project is open source. See the GitHub link in the footer.