CAPTCHAs Kit

Generate and validate CAPTCHAs on your own server. Image generation, audio fallback, and rate limiting built in. Privacy-first, no tracking.

Stack

• Next.js 16 — API routes for CAPTCHA generation and validation.
• Node.js — Canvas API for server-side image rendering.
• Redis — Session storage and rate limiting.

Features

• Image and audio CAPTCHAs — Generate distorted text images and audio alternatives for accessibility.
• Self-hosted validation — No external API calls. Verify challenges on your own infrastructure.
• Rate limiting — Built-in Redis integration to prevent brute-force attacks and abuse.

Install

git clone https://github.com/yashthakur1/cap.git my-captcha
cd my-captcha
npm install

Environment

NEXT_PUBLIC_APP_URL=http://localhost:3000
REDIS_URL=redis://localhost:6379
CAPTCHA_SECRET=your-secret-key-here
SESSION_TIMEOUT=300

Walkthrough

1. Install dependencies

Clone the repo and install packages. Ensure Node.js 18+ is installed.

npm install

2. Set up Redis

Install Redis locally or use a managed service. Update REDIS_URL in .env.local.

# macOS
brew install redis
brew services start redis

# Ubuntu/Debian
sudo apt-get install redis-server
sudo systemctl start redis

3. Configure environment

Copy .env.example to .env.local and set CAPTCHA_SECRET to a random string. This key encrypts CAPTCHA sessions.

4. Run development server

Start the Next.js dev server and visit /captcha/demo to test generation and validation.

npm run dev

Gotchas

• Canvas library requires native dependencies — install build tools (python, make, gcc) if npm install fails.
• Redis must be running before starting the dev server. Check with 'redis-cli ping'.
• CAPTCHA_SECRET must be the same across all server instances for distributed deployments.
• Audio CAPTCHAs use text-to-speech — verify ffmpeg is installed for audio generation.

Why not just build it yourself?

If you need advanced bot detection (behavioral analysis, risk scoring), consider a managed service like hCaptcha or Cloudflare Turnstile. This kit focuses on simple, self-hosted challenge-response.

Links

GitHub

License: MIT