Works on Workers

OpenAPI/Swagger parser. parse() and dereference() work, but validate() fails because it uses ajv internally (code generation). Use for parsing specs, not validation.

View Example

import SwaggerParser from '@apidevtools/swagger-parser';

// Usage: Parse OpenAPI/Swagger specs (validation uses ajv which fails)
const spec = {
  openapi: '3.0.0',
  info: { title: 'My API', version: '1.0.0' },
  paths: { '/users': { get: { responses: { '200': { description: 'OK' } } } } }
};
const parsed = await SwaggerParser.parse(spec);
return { success: true, result: { title: parsed.info.title } };

assert-plus

✅ Works

v1.0.0 19,410,392 weekly downloads validation

Extra assertions on top of Node.js assert module - provides type checking utilities

View Example

import assert from 'assert-plus';

// Usage:
assert.string('hello', 'value');
assert.number(42, 'value');
assert.object({ foo: 'bar' }, 'value');
return { success: true, result: 'All assertions passed' };

async-validator

✅ Works

v4.2.5 1,297,309 weekly downloads validation

Async form validation library - commonly used with Ant Design forms

View Example

import Schema from 'async-validator';

// Usage:
const descriptor = {
  name: { type: 'string', required: true, message: 'Name is required' },
  age: { type: 'number', min: 0, max: 120 }
};
const validator = new Schema(descriptor);
const result = await validator.validate({ name: 'Alice', age: 30 });
return { success: true, result };

class-validator

⚠️ Works (with notes)

v0.14.3 5,479,996 weekly downloads validation

Decorator-based validation. Decorators require TypeScript with experimentalDecorators and special bundler config. Consider using zod instead for simpler setup.

💡 Alternative: zod

View Example

import { ValidationError } from 'class-validator';

// Usage: Decorators need TypeScript experimentalDecorators
const err = new ValidationError();
err.property = 'email';
err.constraints = { isEmail: 'must be valid email' };
return { success: true, result: { note: 'Use zod for Workers - decorators need special bundler config' } };

email-validator

✅ Works

v2.0.4 1,119,780 weekly downloads validation

Simple email validation

View Example

import validator from 'email-validator';

// Usage:
const valid = validator.validate('test@example.com');
const invalid = validator.validate('notanemail');
return { success: valid && !invalid, result: { valid, invalid } };

is-url

✅ Works

v1.2.4 7,023,699 weekly downloads validation

Validate if a string is a valid URL

View Example

import isUrl from 'is-url';

// Usage:
const results = [
  isUrl('https://example.com'),
  isUrl('http://example.com/path'),
  isUrl('not a url'),
  isUrl('example.com')
];
return { success: results[0] && results[1] && !results[2] && !results[3], result: results };

joi

✅ Works

v18.0.2 13,183,645 weekly downloads validation

Powerful schema validation with nested objects, arrays, conditionals, custom messages. Works on Workers unlike ajv (which uses new Function).

View Example

import Joi from 'joi';

export default {
  async fetch(request) {
    const userSchema = Joi.object({
      username: Joi.string().alphanum().min(3).max(30).required(),
      email: Joi.string().email().required(),
      age: Joi.number().integer().min(0).max(120),
      role: Joi.string().valid('admin', 'user').default('user')
    });
    
    const body = await request.json();
    const { error, value } = userSchema.validate(body, { abortEarly: false });
    
    if (error) {
      return Response.json({ errors: error.details.map(d => d.message) }, { status: 400 });
    }
    return Response.json({ valid: true, data: value });
  }
};

prop-types

✅ Works

v15.8.1 38,331,118 weekly downloads validation

React PropTypes - runtime type checking for React components

View Example

import PropTypes from 'prop-types';

// Usage:
const stringType = PropTypes.string.isRequired;
const numberType = PropTypes.number;
const objectShape = PropTypes.shape({
  name: PropTypes.string,
  age: PropTypes.number
});
return { 
  success: typeof stringType === 'function' && typeof numberType === 'function',
  result: { hasString: !!stringType, hasNumber: !!numberType, hasShape: !!objectShape }
};

superstruct

✅ Works

v2.0.2 2,973,804 weekly downloads validation

Data validation library

View Example

import { object, string, number } from 'superstruct';

// Usage:
const User = object({ name: string(), age: number() });
try {
  const result = User.create({ name: 'Alice', age: 30 });
  return { success: result.name === 'Alice', result };
} catch (e) {
  return { success: false, result: e.message };
}

valibot

✅ Works

v1.2.0 4,646,764 weekly downloads validation

View Example

import * as v from 'valibot';

// Usage:
const schema = v.object({ name: v.string() });
const result = v.safeParse(schema, { name: 'Alice' });
return { success: result.success, result: result.output };

valid-url

✅ Works

v1.0.9 2,564,044 weekly downloads validation

URL validation

View Example

import validUrl from 'valid-url';

// Usage:
const valid = validUrl.isUri('http://example.com');
const invalid = validUrl.isUri('not a url');
return { success: valid && !invalid, result: { valid, invalid } };

validator

✅ Works

v13.15.26 15,499,361 weekly downloads validation

String validation library

View Example

import validator from 'validator';

// Usage:
const email = validator.isEmail('test@example.com');
const notEmail = validator.isEmail('not-an-email');
return { success: email && !notEmail, result: { email, notEmail } };

yup

✅ Works

v1.7.1 7,907,264 weekly downloads validation

View Example

import * as yup from 'yup';

// Usage:
const schema = yup.object({ name: yup.string().required() });
const result = await schema.validate({ name: 'Alice' });
return { success: true, result };

zod

✅ Works

v4.3.5 67,068,821 weekly downloads validation

View Example

import { z } from 'zod';

// Usage:
const schema = z.object({ name: z.string(), age: z.number() });
const result = schema.safeParse({ name: 'Alice', age: 30 });
return { success: result.success, result: result.data };

Common Questions

Why are so many packages marked "Build/Dev Tool"?

Many popular npm packages are build tools (webpack, babel), test frameworks (jest, mocha), or CLI utilities (chalk, commander) that run during development—not in production. Cloudflare Workers is a runtime environment for production code. These tools still work great for building your Workers project, they just don't run inside Workers themselves.

Can I use Express/Koa/Hapi in Workers?

Yes! As of September 2025, Workers supports node:http server APIs. Use httpServerHandler from cloudflare:node to wrap Express, Koa, or other Node.js HTTP frameworks. For new projects, we recommend lightweight alternatives like Hono or itty-router which are built for edge environments.

What about databases like PostgreSQL or MySQL?

Workers supports database clients like pg (PostgreSQL) and mysql2 when connecting to public endpoints. For production, use edge-optimized solutions: Cloudflare D1 (SQLite), Neon (serverless Postgres), PlanetScale (MySQL), or Upstash Redis.

Why doesn't package X work?

Common reasons: Native modules (C++ bindings like sharp, bcrypt) don't work—use alternatives like bcryptjs or Cloudflare Images. Filesystem access (fs module for local files) isn't available—use KV, R2, or D1 instead. TCP sockets (raw socket.io, redis) aren't supported—use Durable Objects, WebSockets, or HTTP-based alternatives.