Conciseness

The body is lean: a flow-selection table, two focused code blocks, terse security checklists, and a pointer to the reference file. No padding, no explanation of concepts Claude already knows (no 'what is OAuth' prose, no library tutorials). This matches the anchor-5 'lean and efficient; every token earns its place' profile; the only candidate for trimming — the one-line intro restating the description — is negligible.

Actionability

The Express authorization-code flow and PKCE generator are real, largely copy-paste-ready JavaScript with correct parameter construction and state validation. Not anchor 5 because of concrete gaps: the callback ends in a placeholder comment ("// Store tokens securely and create session"), `PROVIDER_URL` is never defined, the imported `jwt` is unused, and the token exchange has no error handling for a failed `tokenResponse`. Above anchor 3 because the code is genuinely executable rather than pseudocode.

Workflow Clarity

The flow table routes the user to the right mechanism, and Step 1/Step 2 sequence the authorization-code flow with an explicit state-validation checkpoint ("if (req.query.state !== req.session.oauthState)"). Not anchor 5 because there is no validation or error-recovery loop after the token exchange — a failed or malformed token response is unhandled. Not capped at 3: auth implementation is not a destructive or batch operation. Anchor 4 ('clear sequence with most checkpoints present; minor validation gaps') is the best fit.

Progressive Disclosure

SKILL.md serves as a clear overview (core flows and security rules) with a well-signaled, one-level-deep reference: "See [references/python-java.md](references/python-java.md) for:" followed by a bullet list of exactly what it contains. The reference file exists, matches those bullets, and contains no further nested references. The split is appropriate — main JS flow inline, Python/Java/OIDC-provider details external — matching the anchor-5 example structure.

Specificity

The description names the domain ("OAuth 2.0 and OpenID Connect") and concrete specifics ("authorization code flow, PKCE, token refresh, scope management"), but the leading capability statement "authentication with secure flows" is generic — there is no concrete action verb like 'implement', 'configure', or 'integrate'. This matches anchor 3 (names domain and 1-2 concrete actions, not comprehensive); it is above anchor 2 because the flow/scope terms are specific, and below anchor 4 because the actual actions to perform are never stated, only topics are enumerated.

Completeness

Both questions are answered explicitly: what ("OAuth 2.0 and OpenID Connect authentication with secure flows") and when ("Use for third-party integrations, SSO systems, token-based API access, or encountering authorization code flow, PKCE, token refresh, scope management errors"). This mirrors the anchor-5 example structure — clear what followed by an explicit, concrete 'Use when' clause with multiple trigger phrases.

Trigger Term Quality

Good natural trigger coverage: "third-party integrations", "SSO systems", "token-based API access", "token refresh", "scope management" — phrases a user would plausibly say. Not anchor 5 because common variations like "login", "sign-in with...", "social login", or simply "OAuth"/"OIDC" as standalone user utterances are absent; above anchor 3 because multiple synonyms across integration scenarios are present.

Distinctiveness Conflict Risk

Terms like "authorization code flow", "PKCE", and "scope management" form a clear niche with minimal conflict risk. Below anchor 5 because "third-party integrations" and "token-based API access" are broad enough to overlap with generic API-integration or JWT/API-key skills; above anchor 3 because the OAuth-specific triggers dominate the description.