anti-bot

WAF (Web Application Firewall)

A WAF is a security layer that inspects and filters HTTP traffic to block malicious requests including automated scrapers.

A Web Application Firewall (WAF) sits between a website and the public internet, examining each inbound request against a set of rules. Rules can block traffic based on IP reputation, request rate, header anomalies, geographic location, or known attack signatures. Modern WAFs from vendors such as Cloudflare, Imperva, and AWS integrate machine-learning models that score each visitor's likelihood of being a bot.

For web scrapers, a WAF is often the first line of defense encountered. The WAF may silently drop requests, return a 403, serve a challenge page, or redirect to a CAPTCHA. Because WAF rules are continuously updated, a scraper that works today may be blocked tomorrow without any code change on the target site.

Bypassing a WAF requires mimicking legitimate browser behaviour at every layer — TLS fingerprint, HTTP header order, request pacing, and JavaScript execution — so that the WAF's scoring model assigns a low bot probability to the session.

Examples

# Detecting a WAF response (simplified)
response = requests.get(url, headers=headers)
if response.status_code in [403, 429]:
    print("Likely blocked by WAF")
elif "cf-ray" in response.headers:
    print("Cloudflare WAF detected")