Ready to supercharge your AI agents?

Install any skill in seconds. Free to start, no credit card required.

Get Started Free →

Coverage Analysis · trailofbits | DecimalAI

testingby trailofbits

Coverage Analysis

trailofbits/coverage-analysis

Source trailofbits/skills ↗License CC-BY-SA-4.0

Coverage analysis measures code exercised during fuzzing.

SkillScore100Maintained

Automatic

Security & AppSec pack

Last verified 8/9/2026

What it changes

Passed 22 of 22 test cases with the skill, and 18 of 22 without it.

Without skill82%

With skill100%

Checks it passed that the model alone missed

specifies using LLVM 18 or newer
defines NO_MAIN for the coverage executable target
uses gcovr --delete to clear existing gcda profile files

and 2 more in the full report

4 fixed18 passed either way0 still failing0 broke

Pass-rate lift: +18 pp
Tokens: +246%
Agent turns: 0%
Response time: -30%

Model gemini-3.6-flashMeasured 8/9/2026v122 of 22 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/trailofbits-coverage-analysis/SKILL.md https://app.decimal.ai/s/trailofbits-coverage-analysis/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add trailofbits-coverage-analysis, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/trailofbits-coverage-analysis/ and pins it in .decimal/skills.lock

decimalai skills add trailofbits-coverage-analysis

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/trailofbits-coverage-analysis/SKILL.md https://app.decimal.ai/s/trailofbits-coverage-analysis/SKILL.md

Raw file: /s/trailofbits-coverage-analysis/SKILL.md ↗ · machine-readable summary at /s/trailofbits-coverage-analysis.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 4 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 4

Prompt

We are evaluating two successive seed batches using a GCC gcov build. After analyzing batch 1, we want to reset the accumulated GCC execution counters before running batch 2. What tool command clears these .gcda files?

What was checked, without and with the skill
Checked	Without skill	With skill
uses gcovr --delete to clear existing gcda profile files	Missed	Passed

case-09 · gemini-3.6-flash · 8/9/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md599 lines2 files

Coverage Analysis

Coverage analysis is essential for understanding which parts of your code are exercised during fuzzing. It helps identify fuzzing blockers like magic value checks and tracks the effectiveness of harness improvements over time.

Overview

Code coverage during fuzzing serves two critical purposes:

Assessing harness effectiveness: Understand which parts of your application are actually executed by your fuzzing harnesses
Tracking fuzzing progress: Monitor how coverage changes when updating harnesses, fuzzers, or the system under test (SUT)

Coverage is a proxy for fuzzer capability and performance. While coverage is not ideal for measuring fuzzer performance in absolute terms, it reliably indicates whether your harness works effectively in a given setup.

Key Concepts

Concept	Description
Coverage instrumentation	Compiler flags that track which code paths are executed
Corpus coverage	Coverage achieved by running all test cases in a fuzzing corpus
Magic value checks	Hard-to-discover conditional checks that block fuzzer progress
Coverage-guided fuzzing	Fuzzing strategy that prioritizes inputs that discover new code paths
Coverage report	Visual or textual representation of executed vs. unexecuted code

When to Apply

Apply this technique when:

Starting a new fuzzing campaign to establish a baseline
Fuzzer appears to plateau without finding new paths
After harness modifications to verify improvements
When migrating between different fuzzers
Identifying areas requiring dictionary entries or seed inputs
Debugging why certain code paths aren't reached

Skip this technique when:

Fuzzing campaign is actively finding crashes
Coverage infrastructure isn't set up yet
Working with extremely large codebases where full coverage reports are impractical
Fuzzer's internal coverage metrics are sufficient for your needs

Quick Reference

Track record

Benchmark

22 / 22

test cases passed, vs 18 / 22 without

Adoption

Users: 4
Times used: 25

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

trailofbits / skills

plugins/testing-handbook-skills/skills/coverage-analysis/SKILL.md

View on GitHub ↗

License CC-BY-SA-4.0Imported 8/3/2026Version v1Bundled 1 file

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

Coverage Analysis

Overview

Key Concepts

When to Apply

Quick Reference

Track record

Benchmark

Adoption

SkillSafety

Source

Related skills