Kolega vs Semgrep

The headline numbers

The technical difference

This is the comparison most worth understanding properly because the two tools look superficially similar (both do “SAST”) but work very differently underneath.

Semgrep is pattern matching. You write (or use community-written) rules that describe what a vulnerability looks like, and Semgrep finds matches in your code. Semgrep Pro added cross-file taint analysis, which extends pattern matching across function boundaries. This is genuinely useful and faster than most semantic analyzers.

The strength of this approach: it's transparent, fast, and you can write custom rules in a syntax that looks like the code you're trying to match. The community contributes rules constantly, so coverage of known vulnerability patterns is broad and updated.

The limitation: it can only find what someone's written a rule for. If a bug doesn't match an existing pattern — because it's a semantic flaw, a business logic error, a race condition, or a BOLA where the auth check is present but the query doesn't filter by the authenticated user — Semgrep won't catch it. There's no rule to match because the bug isn't shaped like a rule.

Kolega is semantic analysis. Rather than pattern matching, Kolega reads the data flow across your entire codebase, understanding what the code is trying to do, where data comes from, what touches it, and what the security implications are. There's no rule database to maintain because the engine reasons about the code directly.

The strength: it catches bugs nobody has written a rule for, including the ones that don't have known patterns yet. This is what produces the RealVuln gap.

The limitation: it's slower than pattern matching on first scan (though incremental scans are fast), and it's not open source.

Feature comparison

When to pick Semgrep

If your team has engineers who want to write and own custom rules for your specific codebase, Semgrep is built for that and Kolega isn't (yet). The ability to write a rule that catches a pattern your team specifically cares about is genuinely valuable.

If you need self-hosted on-prem with no external dependencies, Semgrep Community Edition runs entirely local. Our self-hosted runners exist but only on Enterprise.

If you need language coverage Kolega doesn't have yet — Semgrep supports 30+ languages, we support 12 of the most common ones — Semgrep wins by default.

If you want a tool whose engine you can audit, the Semgrep CLI is open source under LGPL-2.1. Some security teams require that and it's a legitimate requirement.

If you're an early-stage team that fits inside Semgrep's free tier (10 contributors, 50 repos), the free tier is genuinely useful and we're not going to pretend otherwise.

When to pick Kolega

If your priority is catching the vulnerabilities that don't match known patterns — logic flaws, BOLA, race conditions, semantic bugs — Kolega is built specifically for that category. The RealVuln gap (92.4% vs 17.5%) is what this looks like in practice.

If your codebase is increasingly AI-generated and you've noticed pattern-matching SAST is missing the bugs that ship, semantic analysis catches a different class of defect entirely.

If you want autofix PRs that include regression tests proving the fix works, our PR generation is built around that workflow.

If you don't want to maintain a custom rule library, Kolega doesn't require one. The engine reasons about your code without rules.

When to run both

This is more reasonable than it sounds. Semgrep is good at catching pattern-matchable bugs fast, and the custom rules let your team enforce specific organisational standards. Kolega catches the semantic flaws Semgrep can't.

A common stack: Semgrep in CI for fast pattern checks and custom rule enforcement, Kolega on PR open for deep semantic analysis. They don't overlap meaningfully — different engines, different bug classes.

FAQ