Conciseness

The body is dense and assumes competence, but the opening paragraph explains the coverage-guided mutation loop (a concept Claude already knows) and the ASCII routing diagram substantially duplicates the routing table immediately below it. This matches the 4 anchor (efficient with minor over-explanation to trim); it is above 3 because no section is padded, and below 5 because the diagram/table redundancy and concept-explainer could be cut.

Actionability

Real, executable specifics throughout: `-fsanitize=fuzzer,address,undefined -fno-sanitize-recover=all`, `-merge=1` / `afl-cmin`, `./fuzz_target -max_total_time=300 fuzz/corpus fuzz/seeds`, a copy-paste CI YAML block, and named structured-input helpers per engine. Matches the 4 anchor (mostly executable with minor gaps); the gap is that the core authoring task defers entirely - "Exact harness syntax per engine is in the reference files" - leaving no complete inline harness example, which keeps it from 5.

Workflow Clarity

Five explicitly sequenced steps with concrete per-step guidance and some checkpoints ("Run locally until coverage plateaus", "minimise every crash input before filing it", 3-5 min CI smoke bound). Matches the 4 anchor (clear sequence, most checkpoints present); it falls short of 5 because there are no explicit verify/recover feedback loops, e.g. confirming the harness builds and collects coverage before launching a campaign, and above 3 because the sequence and stopping criteria are explicit rather than implicit.

Progressive Disclosure

The umbrella file stays at routing/workflow altitude while all nine referenced files exist, are one level deep (siblings link to each other and back to SKILL.md, never deeper), and are signaled three ways: the engine table, inline at the relevant workflow step, and a closing References list with per-file purpose notes. Matches the 5 anchor (clear overview, well-signaled one-level-deep references, appropriate split).

Specificity

"Picks libFuzzer, AFL++, cargo-fuzz, Go fuzzing, Atheris or Jazzer by language" and "covers fuzz targets, seed corpora, dictionaries, sanitizers, crash triage and CI smoke fuzzing" list multiple concrete actions covering the whole workflow in third-person voice. This matches the 5 anchor (comprehensive concrete actions); it is above 4 because coverage spans every workflow stage with no real gaps.

Completeness

Explicitly answers both questions: "Use when a project needs fuzz testing, a fuzz campaign must be written or maintained, or fuzzer crashes need triage" (when, with three concrete triggers) and the engine-selection plus coverage list (what). Matches the 5 anchor exactly; not 4 because the 'when' clause is explicit rather than merely adequate.

Trigger Term Quality

Natural phrases a user would say are all present: "fuzz testing", "fuzz campaign", "fuzzer crashes need triage", plus the engine names (libFuzzer, AFL++, cargo-fuzz, Atheris, Jazzer) users invoke directly. Matches the 5 anchor for comprehensive natural-term coverage; a 4 would require missing synonyms, and none of the common phrasings are absent.

Distinctiveness Conflict Risk

The fuzz-testing niche is clearly staked out by named engines and fuzzing-specific triggers (campaigns, corpora, crash triage), giving minimal overlap risk with generic testing or debugging skills. Matches the 5 anchor (clear niche with distinct triggers).