semgrep

A Semgrep security scanner that checks source code for patterns associated with vulnerabilities and can produce SARIF results, a standard format for scan findings.

In plain words
What is it for?
Use it to run either a broad scan or a high-confidence security scan on a codebase. It detects languages, runs scans in parallel, and combines the results.
Why use it?
It helps find security problems across supported languages, including issues that span multiple files when Semgrep Pro is available.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/backspace-shmackspace/claude-devkit/semgrep
Any agent
npx skills add backspace-shmackspace/claude-devkit --skill semgrep
Clone the repo
git clone --depth 1 https://github.com/backspace-shmackspace/claude-devkit

Made for: Claude Code, Codex.

Per session 95 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 6,569 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00095 $0.06569
Opus 5 $0.00048 $0.03284
Sonnet 5 $0.00019 $0.01314
Haiku 4.5 $0.00010 $0.00657

Measured 3d ago against content hash 3ad46fa0988f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

semgrep scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Recursive force deletemediumDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

[ -n "[OUTPUT_DIR]" ] && rm -rf [OUTPUT_DIR]/repos

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

skills/semgrep/SKILL.md · 559 lines

How it starts

The opening of the file, as written. The whole thing — 559 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Semgrep Security Scan

Run a Semgrep scan with automatic language detection, parallel execution across language groups, 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 running 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. Run all scan workers in parallel — Parallel execution is the core performance advantage. Do not run language scans strictly one-after-another when independence allows overlap.
  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.

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

  • Binary analysis → Use binary analysis tools
  • Already have Semgrep CI configured → Use existing pipeline
  • Need cross-file analysis but no Pro license → Consider CodeQL as alternative
  • Creating custom Semgrep rules → Use semgrep-rule-creator skill
  • Porting existing rules to other languages → Use semgrep-rule-variant-creator skill

Output Directory

All scan results, SARIF files, and temporary data are stored in a single output directory.

  • If the user specifies an output directory in their prompt, use it as OUTPUT_DIR.
  • If not specified, default to ./static_analysis_semgrep_1. If that already exists, increment to _2, _3, etc.

Read the full file on GitHub · 559 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 559 lines · 95 tokens per session scan B 3ad46fa0988f

Subscribe to this mod's changes

semgrep is a skill published in the GitHub repository backspace-shmackspace/claude-devkit (15 stars, last pushed 9d ago), licensed MIT. It adds 95 tokens to every session and 6,569 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it B with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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