fastify-ata

Fastify plugin for ata-validator - JSON Schema validation powered by simdjson.

Drop-in replacement for Fastify's default ajv validator. Standard Schema V1 compatible.

Install

npm install fastify-ata

Usage

const fastify = require('fastify')()
const fastifyAta = require('fastify-ata')

fastify.register(fastifyAta)

fastify.post('/user', {
  schema: {
    body: {
      type: 'object',
      properties: {
        name: { type: 'string', minLength: 1 },
        age: { type: 'integer', minimum: 0 },
        role: { type: 'string', default: 'user' }
      },
      required: ['name']
    }
  }
}, (req, reply) => {
  // req.body.role === 'user' (default applied)
  reply.send({ ok: true, name: req.body.name })
})

fastify.listen({ port: 3000 })

All your existing JSON Schema route definitions work as-is.

Options

fastify.register(fastifyAta, {
  coerceTypes: true,       // convert "42" → 42 for integer fields
  removeAdditional: true,  // strip properties not in schema
})

Standalone Mode (Pre-compiled)

Drop-in replacement for @fastify/ajv-compiler/standalone. Same API.

const StandaloneValidator = require('fastify-ata/standalone')

// Build phase (once) - compile schemas to JS files
const app = fastify({
  schemaController: { compilersFactory: {
    buildValidator: StandaloneValidator({
      readMode: false,
      storeFunction(routeOpts, code) {
        fs.writeFileSync(generateFileName(routeOpts), code)
      }
    })
  }}
})

// Read phase (every startup) - load pre-compiled, near-zero compile time
const app = fastify({
  schemaController: { compilersFactory: {
    buildValidator: StandaloneValidator({
      readMode: true,
      restoreFunction(routeOpts) {
        return require(generateFileName(routeOpts))
      }
    })
  }}
})

Standard Schema V1

ata-validator natively implements Standard Schema V1 - the emerging standard for TypeScript-first schema libraries.

const { Validator } = require('ata-validator')
const v = new Validator(schema)

// Standard Schema V1 interface
const result = v['~standard'].validate(data)
// { value: data } on success
// { issues: [{ message, path }] } on failure

Works with Fastify v5's Standard Schema support, tRPC, TanStack Form, Drizzle ORM.

What it does

• Registers a custom validatorCompiler using ata-validator
• Applies default values, coerceTypes, removeAdditional during validation
• Caches compiled schemas (WeakMap) for reuse across routes
• Returns Fastify-compatible validation errors on invalid requests (400)
• Works with Fastify v4 and v5

Performance

Real-world HTTP benchmark (autocannon, 10 connections, 5s)

Payload	ata	ajv
1 user (0.1KB)	65.7K req/sec	65.7K req/sec	equal
10 users (0.9KB)	57.2K	55.3K	+3%
50 users (4.6KB)	36.0K	33.8K	+6%
100 users (9.1KB)	24.6K	22.6K	+9%

Where ata really shines

Scenario	ata	ajv
Constructor cold start	1.25M ops/sec	873 ops/sec	1,432x faster
Serverless cold start (50 schemas)	0.1ms	23ms	242x faster
First validation (construct + validate)	15.7K ops/sec	855 ops/sec	18x faster
ReDoS protection (catastrophic pattern)	0.3ms	765ms	immune
Batch NDJSON (10K items, multi-core)	13.4M/sec	5.1M/sec	2.6x faster
validate(obj) valid (isolated)	14.6M ops/sec	8.3M ops/sec	1.8x faster
validate(obj) invalid (isolated)	12.9M ops/sec	8.0M ops/sec	1.6x faster
validateJSON(str) valid	2.1M ops/sec	1.9M ops/sec	1.1x faster
Fastify startup (5 routes)	0.5ms	6.0ms	12x faster
Schema compilation	136K ops/sec	794 ops/sec	171x faster

Things only ata can do

• RE2 regex engine - linear-time guaranteed, immune to ReDoS attacks
• Multi-core parallel validation - NDJSON batch at 12.5M items/sec
• Standard Schema V1 - native support, ajv doesn't have it
• Lazy compilation - near-zero constructor, 1,432x faster cold start
• 171x faster compilation - serverless cold starts, dynamic schemas

License

MIT