Add experimental MCP skills extension support (SEP-2640)#207
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Add experimental MCP skills extension support (SEP-2640)#207
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Implements the experimental `io.modelcontextprotocol/skills` extension as sugar over the existing Resources primitive. Skills are markdown documents (SKILL.md + YAML frontmatter) served under `skill://` URIs, with optional discovery via `skill://index.json`. - `skills-list` reads the well-known index, falling back to scanning resources for `skill://*/SKILL.md` URIs (per spec, an absent index does not imply zero skills) - `skills-get <name>` reads the SKILL.md; `--raw` prints just the markdown for piping to LLMs or files - Session overview surfaces `skills` under capabilities when the server advertises `capabilities.extensions["io.modelcontextprotocol/skills"]` - JSON output is documented for both commands so AI agents can consume it
Coverage: - Unit: parseIndex (well-formed, malformed, drops bad entries, JSON errors), skillsFromResources (URI matching, nested paths, ignores non-skill-md files), resolveSkillUri (bare names, nested paths, full URIs, trailing slashes), extractTextContent, discoverSkills (index path, fallback path, paginated resource scan) - Unit: formatSkills (count, descriptions, types, empty state), formatSkillDetail (markdown body, missing MIME, blob fallback, truncation), formatServerDetails capability surfacing under both `capabilities.extensions` (per spec) and `capabilities.experimental` (SDK-preserved escape hatch) - Unit: parser suggests `skills-list` for `skills`/`list-skills` - E2E: opt-in `WITH_SKILLS=true` server flag exposes skill:// resources and advertises the extension capability. Three scenarios covered: index-path discovery, no-index fallback (`SKILLS_NO_INDEX=true`), and no-extension server. Verifies --json shapes, --raw mode, nested skill paths, full-URI input, and that --json+--raw still emits the full ReadResourceResult so `jq -r '.contents[0].text'` works. Implementation tweak: capability detection now also accepts `capabilities.experimental[skills]` since current MCP SDKs strip unknown capability fields like `extensions`. Test server advertises under both keys for forward compatibility. Internal helpers (parseIndex, skillsFromResources, extractTextContent, discoverSkills) are exported with `@internal` markers for testability.
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Summary
Implements support for the experimental MCP skills extension (
io.modelcontextprotocol/skills, SEP-2640), adding two new CLI commands (skills-listandskills-get) that provide sugar over the existing resources primitive for discovering and reading Agent Skills.Key Changes
New
skillscommand module (src/cli/commands/skills.ts):skill://index.jsonwith fallback to resource scanning forskill://*/SKILL.mdURIslistSkills(): Discovers and lists skills exposed by the servergetSkill(): Reads a skill's SKILL.md content by name or URIresolveSkillUri(): Converts user-friendly skill names to fullskill://URIsCLI integration (
src/cli/index.ts):skills-listcommand with discovery strategy documentationskills-get <name>command with--rawflag for markdown-only outputKNOWN_SESSION_COMMANDSOutput formatting (
src/cli/output.ts):formatSkills(): Renders skill list with names, descriptions, and typesformatSkillDetail(): Displays skill content with URI and MIME type metadataformatServerDetails()to advertise skills capability when server declares the extensionDocumentation:
--rawmodeImplementation Details
skill://index.jsonindex; if unavailable, falls back to scanning all resources forskill://**/SKILL.mdpatterns (per spec requirement to not treat absent index as proof of no skills)git-workflow), nested paths (acme/billing/refunds), and full URIs--rawflag enables piping skill markdown directly to other tools without formatting overheadhttps://claude.ai/code/session_01PyzCAbMiMXTbLrFXUP3nQJ