# Semgrep

Runs a Semgrep security scan over a codebase: detects languages, selects rulesets...

- Repository: https://github.com/trailofbits/skills (7935 stars)
- Category: Security
- License: CC-BY-SA-4.0
- Last updated: 2026-10-28
- Runs scripts: yes, review before use

## Install

Claude Code: `npx skills add trailofbits/skills --skill semgrep -g -a claude-code -y`
Codex: `npx skills add trailofbits/skills --skill semgrep -g -a codex -y`
Cursor: `npx skills add trailofbits/skills --skill semgrep -g -a cursor -y`
Gemini CLI: `npx skills add trailofbits/skills --skill semgrep -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add trailofbits/skills`

## Description

Runs a Semgrep security scan over a codebase: detects languages, selects rulesets, presents the plan for explicit approval, then runs every approved ruleset through scripts/run-scans.sh, which batches the semgrep processes and writes scans.json, and merges the output to SARIF. Supports two scan modes, "run all" for full ruleset coverage and "important only" for security findings at medium-to-high confidence and impact. Uses Semgrep Pro for cross-file taint analysis when it is available. Use when asked to scan code for vulnerabilities, run a security audit with Semgrep, find bugs, or perform static analysis. For the same scan without the approval gate, use the /static-analysis:semgrep-scan workflow.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Semgrep Security Scan

Run a Semgrep scan with automatic language detection, parallel execution, and merged SARIF output.

## Essential Principles

1. **Always use `--metrics=off`**, Semgrep sends telemetry by default; `--config auto` also phones home. Every `semgrep` command must include `--metrics=off` to prevent data leakage during security audits.
2. **User must approve the scan plan (Step 3 is a hard gate)**, The original "scan this codebase" request is NOT approval. Present exact rulesets, target, engine, and mode; wait for explicit "yes"/"proceed" before spawning scanners.
3. **Third-party rulesets are required, not optional**, Trail of Bits, 0xdea, and Decurity rules catch vulnerabilities absent from the official registry. Include them whenever the detected language matches.
4. **`scripts/run-scans.sh` generates the commands; do not write them yourself**, it builds every `semgrep` line from the approved list. That is what makes `--metrics=off`, the `--include` scoping rule, and the parallel dispatch properties of the code rather than instructions. Give it the approved rulesets and let it run.
5. **Always check for Semgrep Pro before scanning**, Pro enables cross-file taint tracking and catches ~250% more true positives. Skipping the check means silently missing critical inter-file vulnerabilities.
6. **Report what did not run**, `scans.json` carries `failed` and `skipped` alongside `scans`. A ruleset whose repo would not clone, or whose scan exited non-zero, must appear in the report. A partial scan presented as a complete one is worse than no scan.

## When to Use

- Security audit of a codebase
- Finding vulnerabilities before code review
- Scanning for known bug patterns
- First-pass static analysis

## When NOT to Use

The rest: https://github.com/trailofbits/skills/blob/HEAD/plugins/static-analysis/skills/semgrep/SKILL.md