What is JSON to Joi Schema Generator?
Joi is the most popular schema validation library for Node.js, used with Express, Hapi, and Fastify to validate API request bodies, query parameters, and configuration objects. Instead of writing Joi schemas by hand from an API response or JSON sample, this tool automatically generates the complete schema — including nested objects, arrays, and type-specific validators like .email() and .integer().
How to Use
- Set the root schema name and module format (ESM or CJS) in the options above
- Paste your JSON data into the input area
- Toggle "Mark all required" to add .required() to all fields, or leave unchecked for .optional()
- Toggle "Detect email format" to automatically add .email() to string fields that look like email addresses
- Click "Generate Joi Schema" to create the schema
- Copy the output and use it in your Node.js project
Why Use This Tool?
Tips & Best Practices
- Use realistic sample data — type inference depends on actual values
- Integer values are mapped to Joi.number().integer(), floats to Joi.number()
- Null values generate Joi.any().allow(null) — adjust to .nullable() if preferred
- The generated schema is a starting point — add .min(), .max(), .pattern() refinements for production use
- With Express, pair Joi schemas with celebrate or express-joi-validation middleware
Frequently Asked Questions
What is Joi?
Joi is a powerful schema description language and data validator for JavaScript. It is widely used in Node.js applications with Express, Hapi, and Fastify to validate request bodies, query parameters, and other input data at runtime.
How does JSON type mapping work with Joi?
JSON strings map to Joi.string(), integers to Joi.number().integer(), floats to Joi.number(), booleans to Joi.boolean(), null to Joi.any().allow(null), arrays to Joi.array().items(Joi.type()), and objects to Joi.object({...}). Nested objects are extracted as separate const schema variables for clarity.
Can I use the generated schema with Express?
Yes! The generated Joi schema works with any Node.js framework. With Express, use it with middleware like celebrate or express-joi-validation. With Hapi, Joi is built-in for route validation. With Fastify, use it via fastify-joi or similar plugins.
Is my data sent to a server?
No, all processing happens entirely in your browser. Your JSON data never leaves your device.