Conciseness

The body is lean — a payload table, ready-to-run curl probes, win signals, and checklists with almost no padding. The two short intro paragraphs ('Header injection turns user-controlled input into HTTP protocol control…', 'The Host header is trusted by application code…') briefly restate concepts Claude already knows, which is the minor over-explanation the score-4 anchor describes; not enough padding to drop to 3.

Actionability

Every section gives copy-paste-ready curl commands with concrete payloads, headers, grep filters, and interpretation of output ('Win signal: X-Injected: crlf-test… appears in the response headers'). The payload encoding table plus per-technique commands cover the common cases exactly as the score-5 anchor requires; the only placeholders (<TARGET>, basic.jar) are legitimately environment-specific.

Workflow Clarity

Each technique follows a probe → check win signal → escalate pattern, the cache-poisoning section has an explicit enumeration loop followed by a step-by-step canary verification ('Now fetch WITHOUT the header — if body still contains canary, it was cached'), and the document closes with a five-item Verification Checklist plus a False Positives section for error recovery. Explicit validation steps, feedback loops, and a checklist match the score-5 anchor; the batch rate-limit loop includes interpretation guidance, so no validation cap applies.

Progressive Disclosure

No bundle files exist (references/, scripts/, assets/ are absent), and the ~225-line single file is organized into clearly labeled, navigable sections covering the full technique catalog. Structure is good and content is mostly appropriately placed, but a payload table and several self-contained technique sections could arguably live in one-level-deep reference files to keep SKILL.md a slimmer overview — the minor organization gap of the score-4 anchor.

Specificity

The description enumerates multiple concrete technique families — 'CRLF/response splitting', 'Host-header cache poisoning', 'X-Forwarded-* abuse', 'Content-Disposition/Set-Cookie injection', and 'password-reset link poisoning via unvalidated header values' — comprehensive coverage of the domain with no vague filler. It matches the anchor for listing multiple specific concrete actions.

Completeness

The 'what' is clear and detailed, but the description field contains no 'Use when…' clause or equivalent explicit trigger guidance — that lives in metadata.when_to_use, outside the evaluated field. Per the rubric guideline, a missing 'Use when' clause caps completeness at 3; the clear 'what' with absent 'when' matches the score-3 anchor.

Trigger Term Quality

Strong natural keywords security testers actually say ('CRLF', 'response splitting', 'cache poisoning', 'password reset', 'X-Forwarded-*'), but a few common variations from the domain are absent from the description itself (e.g. 'header smuggling', 'method override', 'HTTP response splitting' spelled out). Good coverage with a few natural terms missing, matching the score-4 anchor.

Distinctiveness Conflict Risk

A clear niche (HTTP header injection and its named sub-techniques) with distinct trigger vocabulary; it would not plausibly fire for unrelated skills. This matches the score-5 anchor of a clear niche with distinct triggers and minimal conflict risk.