captchakit 0.5.0

Async-first, fully type-hinted, minimal captcha library with adapters for aiogram, FastAPI and Discord.

captchakit

Async-first, fully type-hinted captcha library for Python 3.10+. Zero runtime deps beyond Pillow. Drop-in adapters for FastAPI, aiogram and discord.py.

---

Why another one?

Feature	lepture/captcha	claptcha	multicolorcaptcha	captchakit
Async API	❌	❌	❌	✅
py.typed + mypy strict	⚠️	❌	❌	✅
TTL & attempt tracking	❌	❌	❌	✅ built-in
Pluggable storage	❌	❌	❌	✅ Protocol
Framework adapters	❌	❌	❌	✅ FastAPI · aiogram · discord.py
Runtime deps (core)	+Pillow	+Pillow	+Pillow	+Pillow

Install

pip install captchakit                  # core
pip install "captchakit[fastapi]"       # + FastAPI adapter
pip install "captchakit[aiogram]"       # + aiogram adapter
pip install "captchakit[discord]"       # + discord.py adapter
pip install "captchakit[redis]"         # + Redis storage + rate limiter
pip install "captchakit[postgres]"      # + Postgres storage backend
pip install "captchakit[django]"        # + Django form field + view
pip install "captchakit[metrics]"       # + Prometheus metrics adapter

See ROADMAP.md for what's next.

30-second example

import asyncio
from captchakit import (
    CaptchaManager, ImageRenderer, MemoryStorage, TextChallengeFactory,
)

async def main() -> None:
    manager = CaptchaManager(
        factory=TextChallengeFactory(length=5),
        renderer=ImageRenderer(),
        storage=MemoryStorage(),
        ttl=120.0,
        max_attempts=3,
    )
    challenge_id, png_bytes = await manager.issue()
    # ... show png_bytes to the user, receive their answer ...
    ok = await manager.verify(challenge_id, user_input="ABCDE")
    print("verified" if ok else "wrong answer, more attempts remain")

asyncio.run(main())

FastAPI in 10 lines

from fastapi import Depends, FastAPI
from captchakit import CaptchaManager, ImageRenderer, MathChallengeFactory, MemoryStorage
from captchakit.adapters.fastapi import captcha_router, verify_captcha

manager = CaptchaManager(MathChallengeFactory(), ImageRenderer(), MemoryStorage())
app = FastAPI()
app.include_router(captcha_router(manager, prefix="/captcha"))

@app.post("/register")
async def register(_: None = Depends(verify_captcha(manager))) -> dict[str, bool]:
    return {"ok": True}

Run the bundled demo:

uv run python -m uvicorn examples.fastapi_login:app --reload
# open http://127.0.0.1:8000

Design

┌─────────────────────────────────────────────────┐
│  Adapters (fastapi / aiogram / discord)         │
├─────────────────────────────────────────────────┤
│  CaptchaManager  (public facade)                │
├──────────────┬──────────────┬───────────────────┤
│  Challenge   │  Renderer    │  Storage          │
│  Text / Math │  Image (PIL) │  Memory / Redis   │
└──────────────┴──────────────┴───────────────────┘

• Protocol-based, so you can drop in your own storage (Redis, Postgres, Memcached), your own renderer (SVG, WebP, audio), or your own challenge factory (wordlists, emoji grids, …).
• Constant-time comparison via hmac.compare_digest.
• Crypto-safe randomness via secrets for solution generation.
• CPU-bound Pillow drawing offloaded to a worker thread via asyncio.to_thread, so the event loop never blocks.

Security scope

captchakit is a lightweight human-check, not a bot-farm-grade security layer. It is aimed at Telegram/Discord verification, simple FastAPI registration flows and similar use cases where you just want to raise the cost for casual spam.

For high-value forms (login, payment) use hCaptcha, Cloudflare Turnstile or reCAPTCHA Enterprise in addition. Combine captchakit with proper rate limiting at the edge of your application.

Roadmap

See ROADMAP.md for the full development plan.

Version	Highlights
0.1 ✅	Core + Text/Math challenges + Image renderer + Memory storage + FastAPI
0.2 ✅	aiogram adapter + RedisStorage + EmojiGridChallenge
0.3 ✅	discord.py adapter + WordChallenge + docs site
0.4 ✅	AudioRenderer + Theme presets + i18n + Prometheus metrics
0.5 ✅	PostgresStorage + SVGRenderer + RateLimiter + Django adapter
1.0	Stable API, semver commitment

Contributing

Contributions welcome. Local development:

git clone https://github.com/akerem16/captchakit
cd captchakit
uv sync --all-extras
uv run ruff check .
uv run mypy
uv run pytest

License

MIT — see LICENSE.