Bot traffic, scraping, credential stuffing, automated attacks — these are challenges any modern web app must defend against. While there are many commercial solutions, open-source tools offer transparency, flexibility, and self-hosting control. Here are five notable open-source / freely available anti-bot / bot detection tools worth exploring.
1. SafeLine
Overview
SafeLine is a self-hosted open-source Web Application Firewall (WAF) built by Chaitin Tech. It acts as a reverse proxy to inspect HTTP/HTTPS traffic and block malicious requests, including bots and automated abuse. Its GitHub repo is licensed under GPL-3.0.-
Bot / Anti-Bot Capabilities
- Anti-Bot challenge to differentiate human vs automation tools
- Threat intelligence (shared malicious IP list) to block known bad actors
- Rate limiting, IP blocking, and custom rules to throttle suspicious behavior
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Strengths
- Runs in your own environment (no external dependencies)
- Super neat UI & Continuous updates
- Balanced features for both WAF + Bot defense
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Challenges / Limitations
- The free/community edition have less config options for anti-bot challenge
- Documentation is less mature and detailed.
Live Demo: https://demo.waf.chaitin.com:9443/statistics
2. BotD
Overview
BotD is an open-source JavaScript library for basic bot detection on the client side, provided under an MIT license.
It helps web apps detect non-browser automation, headless tools, or suspicious clients.-
How It Works
- Runs in the browser context, collecting signals (navigator attributes, behaviors)
- Returns a score or classification (likely bot / not bot)
- Developers can integrate with server side logic to block or challenge flagged traffic
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Pros
- Lightweight, easy to integrate
- Maintained by an established fingerprint / browser profiling team
- Good first line of client-side filtering
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Cons
- It is limited to client-side heuristics, not a full WAF
- Bots can attempt to mimic real browser signals or inject noise
- Must be complemented with server-side defenses
3. Anubis
Overview
Anubis is a newer open-source project designed to protect websites from scraping and AI bots. It offers a challenge mechanism (proof-of-work / JS challenge) before letting traffic through.
It is often used by open-source projects and Git repos under heavy load from crawlers and automated scrapers.-
Key Features
- Adds a pre-check page / challenge before users access the resource
- Helps reduce abusive scraping while preserving performance
- MIT licensed and actively developed
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Strengths
- Good at scraper mitigation, especially for static or semi-static content
- Low overhead, easy to deploy as a middleware in front of web servers
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Limitations
- May introduce friction for legitimate users (challenge steps)
- Not a full bot detection engine (fewer behavioral heuristics)
- More suitable for protecting content / API endpoints than deep interactive apps
4. open-appsec
Overview
open-appsec is an open-source WAF / bot defense solution with ML-based threat protection built for modern web apps and APIs.
It aims to proactively defend against OWASP Top 10, zero-day vulnerabilities, and automated attacks.-
Bot Mitigation Features
- Machine-Learning / anomaly detection for behavior-based classification
- Real-time blocking, auto-adjusting policies
- Integration with Kubernetes, Nginx, GraphQL, and more
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Strengths
- More adaptive than static rule-based systems
- Good integration with modern cloud / container infrastructure
- Open source gives you freedom to extend
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Challenges
- ML models may produce false positives or need tuning
- Requires more resources (CPU/memory) compared to simpler rule-based systems
- Community / documentation may be less mature compared to established projects
5. Fail2Ban (Log-based IP Blocking)
Overview
Fail2Ban is not a bot detection engine per se, but an intrusion prevention tool. It monitors logs (SSH, web logs, etc.) and bans IPs that show malicious behavior (failed login attempts, repeated suspicious requests).-
How It Helps vs Bots
- Blocks brute-force / credential stuffing bots
- Works based on patterns in logs (e.g. too many 404s, repeated login failures)
- Can be integrated with firewalls (iptables, ufw) to block IPs
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Pros
- Lightweight and widely used
- Good as a complementary layer for automated attack blocking
- Easy to configure custom filters for web server logs
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Cons
- Not specialized for web crawling or advanced bot behavior
- Reactive, not proactive — only bans after detection
- Less suited for high-volume requests or stealthy bots
⚖️ Choosing the Right Tool: What Fits Your Needs?
| Scenario / Need | Good Option(s) | Notes |
|---|---|---|
| Full WAF + Bot protection in one | SafeLine, open-appsec | Can handle web attacks & bot detection together |
| Lightweight client-side filtering | BotD | Use it early to drop obvious bots |
| Scraper mitigation / content protection | Anubis | Good for static/edge protection |
| Behavior / anomaly detection | open-appsec (ML) | Useful for subtle / adaptive bots |
| Reactive IP blocking / brute force | Fail2Ban | Simple and effective for credential bots |
⚠️ Best practice: combine multiple layers — client-side detection, WAF + bot rules, rate limiting, challenge pages, and reactive IP banning — to build a robust defense.
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