semgrep
by trailofbitsSemgrep skill for static analysis on codebases with automatic language detection, parallel workers, merged SARIF output, and plan-first approval. Built for semgrep for Security Audit workflows, it supports run all and important only modes, uses --metrics=off, and can leverage Semgrep Pro when available.
This skill scores 78/100, which is solidly listable for directory users. The repository provides real workflow guidance, explicit safety gates, and reusable Semgrep execution logic, so an agent can trigger and run it with less guesswork than a generic static-analysis prompt. Users should still expect to read the workflow docs before installing, because the scan setup is opinionated and multi-step.
- Strong operational guidance: the skill defines a 5-step scan workflow, including language detection, plan approval, execution, and results merging.
- Good agent leverage: it supports parallel subagents, automatic Pro detection, and merged SARIF output for multi-language codebases.
- Useful decision support: references enumerate rulesets and scan modes, helping users choose between full coverage and high-confidence scans.
- No install command in SKILL.md, so setup/adoption may require more manual interpretation than a turnkey skill.
- The workflow is fairly opinionated and gated by explicit user approval before scanning, which may slow simple one-off runs.
Overview of semgrep skill
What semgrep does
The semgrep skill runs Semgrep static analysis across a codebase with language detection, parallel workers, and merged results. It is built for a real security-audit workflow: finding vulnerabilities, risky patterns, and bugs faster than a one-off manual scan.
Who should use it
Use the semgrep skill if you need a practical semgrep for Security Audit, want a repeatable scan process, or need help deciding which rulesets and scan mode fit the repo. It is especially useful on multi-language projects where parallel execution and curated rulesets save time.
What makes it different
This skill is not just “run Semgrep.” It bakes in scan planning, approval gates, --metrics=off, support for Pro when available, and result merging. That matters when you care about audit quality, privacy, and fewer false starts during semgrep usage.
How to Use semgrep skill
Install and locate the workflow
For semgrep install, add the skill from the repo path in your skills system, then read SKILL.md first. Next inspect references/rulesets.md, references/scan-modes.md, references/scanner-task-prompt.md, and workflows/scan-workflow.md before you run anything. Those files explain the decision rules, not just the command syntax.
Give the skill the right input
A strong prompt should include the target repo, whether you want a full audit or only high-confidence findings, and any constraints like offline scanning or CI-friendly output. For example: “Scan this Python and JavaScript repo for security issues, prefer important-only mode, and prioritize secrets, injection, and auth flaws.” That is better than “run semgrep” because it tells the skill how to choose rulesets.
What the scan flow expects
The semgrep guide uses a plan-first workflow: detect languages, select mode and rulesets, present the plan for approval, then execute scans and merge results. In practice, that means you should expect a confirmation step before scanning starts. If you skip approval, the workflow should stop rather than guess.
Practical tips that improve output
Always include the intended target directory if you have one, and be explicit about whether you want breadth or precision. For security audits, important-only reduces noise; for deeper review, run all gives wider coverage. If the repo has languages with known security ecosystems, the skill can combine official and third-party rulesets for better coverage.
semgrep skill FAQ
Is semgrep good for first-time users?
Yes, if you want a guided scan instead of hand-writing a complex command. The semgrep skill reduces setup friction by choosing a workflow, but you still need to confirm the scan plan before execution.
How is this different from a normal Semgrep prompt?
A generic prompt usually asks for a scan and leaves the model to improvise rulesets, severity handling, and result merging. This skill adds explicit process controls, safer defaults like --metrics=off, and a repeatable path for semgrep usage on real repos.
When should I not use it?
Do not use this skill if you only need a quick syntax check, a tiny ad hoc rule test, or a non-security code review. If you already know the exact command and ruleset, the skill may be more process than you need.
Does it fit all repos?
It fits best on source code repositories where static analysis can detect language-specific security patterns. It is less useful for documentation-only projects, binary-heavy repos, or cases where there is no clear code target to scan.
How to Improve semgrep skill
Be specific about the audit goal
The best results come from stating what you care about most: secrets, injection, auth, insecure transport, or broad vulnerability discovery. “Find high-confidence security issues in the API layer” is stronger than “look for problems,” because it helps the semgrep skill select rules and reduce irrelevant findings.
Provide repo facts that affect rule choice
Tell the skill which languages, frameworks, or deployment surfaces matter. A Python monolith, a Java microservice, and a frontend-only app need different rule priorities. This is where semgrep for Security Audit gets materially better: rule choice should follow attack surface, not habit.
Watch for common failure modes
The main risks are overbroad scans, noisy outputs, and skipping the approval gate. If you see too many low-value findings, switch from run all to important-only or tighten the request around one subsystem. If the scan seems incomplete, check that the repo tree was read and the planned rulesets match the detected languages.
Iterate after the first scan
Use the first run to identify which categories produced useful findings, then ask for a second pass focused on those areas. For example, after a broad scan, you might request: “Rerun semgrep on the auth and dependency-loading paths only, keep security rules, and exclude style checks.” That kind of refinement usually beats restarting from scratch.