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testland/mull-mutation

Use for any question about mutation testing in C or C++, or when a C/C++ suite has high coverage but bugs still ship: sets up Mull for Clang builds (version-matched package, -fpass-plugin flags, CMake, mull-runner, mutators, path filters) and runs it in GitHub Actions. Other languages: stryker-mutation, stryker-net-mutation, pitest-mutation, mutmut-mutation.

Quality

88%

Does it follow best practices?

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SecuritybySnyk

Passed

No findings from the security scan

Overview
Quality
Evals
Security
Files

Quality

Content

75%Weight 40%Scale 1-5

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

A well-structured, highly concrete skill: every step carries executable commands, the version-matching gotcha is handled as a first-class concern, and anti-patterns plus limitations are honest and specific. The consistent weaknesses are minor — a padded Overview, a non-copy-paste Linux install step, and no explicit verification checkpoint in the workflow.

Suggestions

Replace the 'install per the official guide' comment in Step 1 with the actual apt commands for the version-matched mull-19 + clang-19 packages, since Linux is the primary platform for CI usage.

Trim the Overview's README block-quotes and paper citation to one or two lines, keeping only the LLVM-IR foundation claim that justifies the 'When to use' fallback for other LLVM languages.

Add an explicit validation checkpoint early in the workflow (e.g., confirm `mull-runner-19 --version` and `clang-19 --version` agree before the CMake build) so version-mismatch failures are caught before a long build.

DimensionReasoningScore

Conciseness

The bulk is lean operational content (numbered steps, executable commands, tables), but the Overview block-quotes the README and cites the 2018 paper — roughly 20 of ~205 lines of over-explanation that could be trimmed. Version numbers (mull-19, 0.34.0) are operationally necessary since version-matching is the core gotcha, so they are not gratuitous time-sensitivity.

4 / 5

Actionability

Nearly all guidance is executable: full CMake invocation with plugin flags, mull-runner commands with reporter and filter flags, CI YAML, and git-diff scoping. The gap is the Linux/Ubuntu install — the primary platform for a CI-oriented LLVM tool — which only points to the official guide URL instead of copy-paste apt commands.

4 / 5

Workflow Clarity

Steps 1-7 are clearly sequenced and cross-referenced (e.g., 'Build with -O0 -g (Step 2)'), and the anti-patterns table preemptively addresses failure modes. However, there is no explicit validation checkpoint (e.g., verifying mull-runner-19 matches the clang version before building) or error-recovery loop, so it falls short of anchor 5.

4 / 5

Progressive Disclosure

No bundle files exist; the single-file body has clean section structure and a References section with annotated, one-level-deep external links. Minor gaps: at ~205 lines, the CI integration or mutator catalog could live in separate reference files, and in-body citations like [mull-tutorial] are only defined at the bottom, so it does not reach anchor 5's well-split structure.

4 / 5

Total

16

/

20

Passed

Description

95%Weight 40%Scale 1-5

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

A strong description with an explicit 'Use for...' trigger clause covering both direct questions and the natural symptom phrasing, a concrete capability list, and explicit cross-language delegation that minimizes sibling-skill conflicts. The only minor gap is that the action list is component-heavy rather than enumerating many distinct actions.

DimensionReasoningScore

Specificity

Enumerates several concrete components ('version-matched package, -fpass-plugin flags, CMake, mull-runner, mutators, path filters') plus 'runs it in GitHub Actions', but the distinct verbs are limited to setting up and running, short of anchor 5's comprehensive multi-action coverage.

4 / 5

Completeness

Explicitly answers both: what ('sets up Mull for Clang builds... and runs it in GitHub Actions') and when ('Use for any question about mutation testing in C or C++, or when a C/C++ suite has high coverage but bugs still ship') with concrete trigger phrases.

5 / 5

Trigger Term Quality

Natural user phrasing is comprehensive: 'mutation testing', 'C or C++', 'C/C++ suite', 'Clang', and the symptom-based trigger 'high coverage but bugs still ship' — exactly what a user would say when they need this skill.

5 / 5

Distinctiveness Conflict Risk

Clear niche (C/C++ mutation testing with Mull) and it actively reduces conflict by delegating other languages to named sibling skills ('stryker-mutation, stryker-net-mutation, pitest-mutation, mutmut-mutation').

5 / 5

Total

19

/

20

Passed

Validation

100%

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation — 16 / 16 Passed

Validation for skill structure

No warnings or errors.

Reviewed

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