is-crawler 1.0.3

Tiny, zero-dependency crawler detection via regex.

is-crawler

Tiny, zero-dependency Python library that detects bots and crawlers from user-agent strings. Fast, lightweight, and ready to drop into any web app or API.

Docs & live demo: is-crawler.tn3w.dev

Install

pip install is-crawler

For faster regex matching, optionally install google-re2. It will be used automatically when available:

pip install is-crawler google-re2

Usage

from is_crawler import is_crawler

is_crawler("Googlebot/2.1 (+http://www.google.com/bot.html)")  # True
is_crawler("Mozilla/5.0 (Windows NT 10.0; Win64; x64) Chrome/120.0.0.0 Safari/537.36")  # False

The module itself is also callable, so you can skip the named import:

import is_crawler

is_crawler("Googlebot/2.1 (+http://www.google.com/bot.html)")  # True

To see which rules matched, use crawler_signals:

from is_crawler import crawler_signals

crawler_signals("Googlebot/2.1 (+http://www.google.com/bot.html)")
# ['bot_signal', 'no_browser_signature']

crawler_signals("Mozilla/5.0 (Windows NT 10.0; Win64; x64) Chrome/120.0.0.0 Safari/537.36")
# []

Possible signal names: bot_signal, no_browser_signature, bare_compatible, known_tool.

Works great as middleware, rate-limiter input, or analytics filter:

from is_crawler import is_crawler

@app.before_request
def block_bots():
    if is_crawler(request.headers.get("User-Agent", "")):
        abort(403)

How it works

Four fast regex checks, no database or external lookups:

1. Bot signals -- common keywords (bot, crawl, spider, scrape, ...), URL/email patterns, headless
2. Missing browser signature -- real browsers always include engine tokens like WebKit, Gecko, or Trident
3. Bare (compatible; ...) block -- classic bot pattern without OS tokens
4. Known tools -- playwright, selenium, wget, lighthouse, sqlmap, and more

Need more?

If you need deeper user-agent analysis -- device type, OS, browser version, or full bot fingerprinting -- check out cr-ua.

License

Apache-2.0