js-perf-investigation

Structured performance opportunity investigation for SpiderMonkey (the Firefox JavaScript engine). Use this skill when the user wants to investigate JS engine performance, profile SpiderMonkey, find optimization opportunities, write performance patches, or evaluate benchmark regressions. Trigger on mentions of: profiling JS, SpiderMonkey performance, JIT optimization, benchmark regression analysis, shell benchmarking, or any request to make JS workloads faster. The methodolgy is described mostly for the JS shell but can be adapted to browser investigation.

Quality

86%

Does it follow best practices?

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Securityby

Passed

No findings from the security scan

Quality

Content

85%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 rich, highly actionable, well-sequenced workflow with strong validation feedback loops, but the body leans long and references a non-existent bundle file, weakening progressive disclosure and slightly undercutting conciseness.

Suggestions

Create the referenced references/advanced-tools.md (or remove the 'see references/advanced-tools.md' pointer) so progressive-disclosure references resolve to real files.

Tighten preamble sections that re-explain fundamentals Claude already knows (e.g. why profilers need enough samples, why debug builds distort profiles) to lift conciseness toward lean.

Consider moving the statistical-evaluation script and the pref-gating recipe into separate reference files so the SKILL.md body reads as a concise overview with well-signaled one-level-deep references.

Dimension	Reasoning	Score
Conciseness	Mostly efficient and assumes Claude's competence with executable commands and minimal preamble, but a few sections (e.g. explaining why statistical profilers need samples, restating the anti-patterns) over-explain slightly and could be trimmed.	4 / 5
Actionability	Fully executable, copy-paste-ready code and commands throughout — samply invocation, mozconfig, pref YAML, instrumentation snippets, hyperfine/seq loops, and a runnable scipy Mann-Whitney script — covering the common cases concretely.	5 / 5
Workflow Clarity	Clear four-phase sequence with explicit validation checkpoints (run jit-test/jstests before commit, re-profile the patched build, Mann-Whitney significance gate, 20-run cap) and feedback loops for error recovery, matching the top anchor for a risky/batch workflow.	5 / 5
Progressive Disclosure	No references/ or scripts/ bundle exists, so the single 'see references/advanced-tools.md' pointer in the body references a file that is absent; structure is one inlined monolith with a dangling reference rather than a clean overview pointing to real one-level-deep files.	3 / 5
	Total	17 / 20 Passed

Description

87%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, well-targeted description that clearly states both the skill's purpose and its trigger conditions with concrete, natural phrasing. Minor room for tighter keyword coverage, but overall distinct and actionable.

Dimension	Reasoning	Score
Specificity	Names the domain and several concrete actions — 'investigate JS engine performance', 'profile SpiderMonkey', 'find optimization opportunities', 'write performance patches', 'evaluate benchmark regressions' — with minor gaps in coverage rather than full comprehensiveness.	4 / 5
Completeness	Explicitly answers both what ('Structured performance opportunity investigation for SpiderMonkey') and when ('Use this skill when... Trigger on mentions of...') with concrete trigger phrases, matching the top anchor.	5 / 5
Trigger Term Quality	Good coverage of natural trigger phrases ('profile SpiderMonkey', 'JIT optimization', 'benchmark regression analysis', 'shell benchmarking') that users would plausibly say, though a few common synonyms or .js-style cues are missing.	4 / 5
Distinctiveness Conflict Risk	Targets a clear niche (SpiderMonkey / Firefox JS engine performance) with distinct, domain-specific triggers that are unlikely to collide with other skills.	5 / 5
	Total	18 / 20 Passed

Validation

87%

Warnings & errors only

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

Validation — 14 / 16 Passed

Validation for skill structure

Criteria	Description	Result
allowed_tools_field	'allowed-tools' contains unusual tool name(s)	Warning
referenced_paths_exist	Referenced path issues: 1 missing	Warning

	Total	14 / 16 Passed

Repository: mozilla/enterprise-firefox
Path: .agents/skills/js-perf-investigation/SKILL.md
Commit: cd7d47c

Reviewed: 3 days ago

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