@jetio/fastify-validator

JetValidator integration for Fastify - 19x faster schema compilation

Drop-in replacement for Fastify's default AJV validator with significantly faster compilation and additional features.

Why?

Fastify uses AJV by default for schema validation. While AJV is excellent, schema compilation can be slow in serverless environments where every millisecond counts.

Compilation speed matters for:

• ✅ Serverless cold starts (Lambda, Cloud Functions)
• ✅ Applications with many routes
• ✅ Dynamic schema generation
• ✅ Fast server restarts

Performance

Compilation speed:

• AJV: ~28ms per schema
• JetValidator: ~1.4ms per schema
• 19x faster on average

See benchmarks

For 20 routes:

• AJV: ~560ms compilation time
• JetValidator: ~28ms compilation time
• 532ms faster cold start

Installation

npm install @jetio/fastify-validator

Usage

Using createJetValidatorController

import Fastify from 'fastify';
import { createJetValidatorController } from '@jetio/fastify-validator';

const fastify = Fastify({
  schemaController: createJetValidatorController({})
});


// Define routes with schemas as usual
fastify.post('/user', {
  schema: {
    body: {
      type: 'object',
      properties: {
        name: { type: 'string', minLength: 2 },
        email: { type: 'string', format: 'email' },
        age: { type: 'number', minimum: 0 }
      },
      required: ['name', 'email']
    }
  }
}, async (request, reply) => {
  return { success: true, user: request.body };
});

fastify.listen({ port: 3000 });

Using createJetValidatorCompiler

import Fastify from 'fastify';
import { createJetValidatorCompiler } from '@jetio/fastify-validator';

const fastify = Fastify({
  schemaController: {
    compilersFactory: {
      buildValidator: createJetValidatorCompiler({}),
    },
  }
});


// Define routes with schemas as usual
fastify.post('/user', {
  schema: {
    body: {
      type: 'object',
      properties: {
        name: { type: 'string', minLength: 2 },
        email: { type: 'string', format: 'email' },
        age: { type: 'number', minimum: 0 }
      },
      required: ['name', 'email']
    }
  }
}, async (request, reply) => {
  return { success: true, user: request.body };
});

fastify.listen({ port: 3000 });

This is for those who wants just the buildValidator and not the entire schema controller.

Options

All JetValidator options are supported for both createJetValidatorController and createJetValidatorCompiler:

createJetValidatorController({
  allErrors: true,        // Collect all errors
  removeAdditional: true, // Remove extra properties
  coerceTypes: true,      // Auto-convert types
  useDefaults: true,      // Apply default values
  validateFormats: true,  // Enable format validation
  $data: true,            // Enable $data references
  errorMessage: true,     // Custom error messages
  strict: true,            // Strict validation mode
  async: true,
  inlineRefs: false,

  //And more.


  //Including 
  errorFormatter?: (errors: any[]) => Error; // Not in jet validator but needed in fastify.
  //Custom Function for formating jet validator errors.
})

Features

Everything Fastify + AJV supports, plus:

• ✅ 19x faster compilation
• ✅ Full JSON Schema Draft 06-2020-12 support
• ✅ 99.2% spec compliance
• ✅ Json Schema Compliant TypeScript type inference (with @jetio/schema-builder)
• ✅ elseIf conditionals
• ✅ Inbuilt formats and custom error messages
• ✅ Advanced $data references
• ✅ Custom keywords (3 types)
• ✅ Macro system
• ✅ Zero dependencies
• ✅ Meta schema system and cli
• ✅ Advance $ref resolution
• ✅ Stand alone code generation that inlines everything and supports custom keywords

Migration from Deafult Fastify Compiler

Zero code changes to your routes. Just change the Fastify initialization:

const fastify = Fastify();
+ import { createJetValidatorController } from '@jetio/fastify-validator';
+ 
+ const fastify = Fastify({
+   schemaController: createJetValidatorController()
+ });

Everything else stays the same.

Examples

See the examples directory:

• basic.js - Basic usage
• comparison.js - Compilation speed comparison

Note on Async Validation: While JetValidator supports async validation natively, it is not supported in this Fastify integration. Per Fastify's own recommendation, async logic such as database lookups during validation can lead to Denial of Service vulnerabilities and unhandled promise rejections. Use Fastify's preHandler hooks for async validation tasks instead.

Compatibility

• Fastify: 4.x, 5.x
• Node.js: 16+

🔗 Links

• JetValidator - Main validator
• Benchmarks - Performance details
• Complete Documentation (20k+ lines) - Main validator full documentation
• Issue Tracker
• GitHub Discussions

📄 License

MIT © Great Venerable

Built with ❤️ for developers who demand full JSON Schema compliance and blazing-fast Fastify startup times.

The Venerable Supreme