semgrep

semgrep is a skill for Claude Code, Codex from stefaniuk/loadout. It costs 151 tokens per session (3,542 once invoked), scanned A, original, MIT.

A Semgrep-based security scanning workflow. Semgrep is a code analysis tool that searches source code for patterns linked to vulnerabilities.

In plain words
What is it for?
Use it to scan a codebase with approved security rules and produce SARIF results, a standard format for reporting code-analysis findings.
Why use it?
It organizes language detection, rule selection, approval, and result merging while disabling Semgrep telemetry during scans.

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/stefaniuk/loadout/semgrep
Any agent
npx skills add stefaniuk/loadout --skill semgrep
Clone the repo
git clone --depth 1 https://github.com/stefaniuk/loadout

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for semgrep

README.md
[![agentmods](https://agentmods.dev/badge/skills/stefaniuk/loadout/semgrep.svg)](https://agentmods.dev/skills/stefaniuk/loadout/semgrep)
Your own site
<a href="https://agentmods.dev/skills/stefaniuk/loadout/semgrep"><img src="https://agentmods.dev/badge/skills/stefaniuk/loadout/semgrep.svg" alt="Measured on agentmods" height="20"></a>
Per session 151 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,542 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. 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 $0.00151 $0.03542
Opus 5 $0.00076 $0.01771
Sonnet 5 $0.00030 $0.00708
Haiku 4.5 $0.00015 $0.00354

Measured 3d ago against content hash aa907e098c45, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

semgrep scanned grade A with 0 findings 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.

The scan reads SKILL.md. This mod also ships 3 executable files (scripts/merge_sarif.py, scripts/run-scans.sh, scripts/test_merge_sarif.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/skills/semgrep/SKILL.md · 263 lines

How it starts

The opening of the file, as written. The whole thing — 263 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, 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 runscans.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

  • 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

Read the full file on GitHub · 263 lines

Files

What ships with it

8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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 · 263 lines · 151 tokens per session scan A aa907e098c45

Subscribe to this mod's changes

semgrep is a skill published in the GitHub repository stefaniuk/loadout (1 stars, last pushed yesterday), licensed MIT. It adds 151 tokens to every session and 3,542 once invoked, about $0.0008 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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