When you write code, bugs are expected. But security vulnerabilities? Those can cost you.

Security issues open the door to exploits, data leaks, and even complete system breaches.

The good news is, you don’t need to spend a fortune to secure your code. Open source tools can do the job well — and they’re free.

I’ve picked five of the best ones you can start using right now. Let’s break down what each one does, why it matters, and how it fits into your workflow.

Semgrep — Fast, Flexible Static Analysis

GitHub: https://github.com/returntocorp/semgrep

Think of Semgrep like a security-aware search engine for your code.

It scans source files quickly, and checks them against rules that look for common bugs, misconfigurations, and vulnerable patterns.

What makes Semgrep stand out is how easy it is to customize. You can write your own rules in YAML. These rules are readable, even for folks who don’t know formal parsing systems.