Conciseness

The body is dense and assumes competence — no basic-concept explanations, just a trigger matrix, three decision flowcharts, three tight code examples, and a corrections table. However, there is trimmable redundancy: the 'Related Skills' and 'Preserved references' sections repeat pointers already given in 'Reference Files' (e.g. evaluation-guide.md and claude-code-mcp-integration.md each appear twice), and the per-version feature enumerations in 'Version Gating' (3.1/3.2/3.3) run long inline. Anchor 5 requires every token to earn its place; these duplications fall just short. Not anchor 3 — the verbosity is isolated, not 'some unnecessary explanation' throughout.

Actionability

All quick-start code is executable and copy-paste ready (minimal server, mount() composition, task=True background tool with the v4 TasksExtension registration), commands are concrete ('uv add fastmcp>=4.0', 'fastmcp run server.py:mcp'), and the mermaid charts give exact API calls per decision branch. The common cases are covered with real code, matching the anchor-5 example.

Workflow Clarity

The core workflow is clearly sequenced: match user intent via the trigger matrix → load the listed reference → 'Generate only the v3 form, then check migration.md for a v3→v4 change', plus an explicit validation checkpoint ('Before deploying: run in-process pytest using the in-memory Client transport... before switching to HTTP transport'). Not anchor 5 because there are no error-recovery/feedback loops after validation fails (e.g. what to do when the in-process tests fail), though as a navigation-style skill the risk is lower than for the destructive/batch contexts the cap targets.

Progressive Disclosure

Scored against the actual bundle: all 17 files listed in the body exist under references/, and no reference file points to another reference (one level deep), with scripts/ correctly reached via references/evaluation-guide.md. SKILL.md is a pure, well-signaled index — a 28-row intent→file trigger matrix plus an annotated file listing with per-file content summaries — making navigation essentially effortless, matching the anchor-5 structure.

Specificity

The description enumerates concrete actions across the full framework lifecycle — 'building, extending, or debugging FastMCP v4 (or v3) Python MCP servers', 'tool/resource/prompt creation', 'provider and transform implementation (CodeMode, Tool Search)', 'auth setup (MultiAuth, PropelAuthProvider, KeycloakProvider)', 'client SDK usage', 'FastMCPApp and Generative UI server building', 'nginx reverse proxy deployment', 'OTEL observability, testing, and v3→v4 migration' — comprehensive, not vague. Anchor 4 would require minor gaps in coverage; none are evident.

Completeness

Both questions are explicitly answered: 'when' via the leading 'Use when building, extending, or debugging...' clause and 'Activates on...' trigger enumeration, and 'what' via the enumerated capabilities (tool creation, auth setup, app building, deployment, migration). This matches the anchor-5 good example structure ('Extract... Use when...') with concrete trigger phrases throughout.

Trigger Term Quality

Natural user phrasing is thoroughly covered: 'building, extending, or debugging' (action synonyms), 'v4 (or v3)' (version synonyms), plus the terms a user would actually say when needing the skill — 'nginx reverse proxy', 'auth setup', 'client SDK', 'testing', 'migration', and specific feature names (CodeMode, MultiAuth, Prefab Apps, OTEL). Not anchor 4, since no commonly used natural term for this domain is missing; file extensions are not relevant to a framework skill.

Distinctiveness Conflict Risk

A clear niche — FastMCP v3/v4 Python MCP servers specifically — with framework- and feature-specific triggers (FastMCP, MultiAuth, KeycloakProvider, FastMCPApp, fastmcp-slim) that no generic Python, MCP, or TypeScript skill would match. Minimal conflict risk; not anchor 4 because there is no meaningful overlap with a closely related skill's trigger space.