Skill of the day: `mcp-builder` (build MCP servers that agents can use)
Official Anthropic mcp-builder skill: four-phase MCP server guide (TS MCP SDK / Python FastMCP). Install via example-skills.
mcp-builder is an official Anthropic marketplace skill shipped inside the example-skills plugin. It guides Deep research & planning → Implementation → Review & test → Evaluations so new MCP servers expose tools agents can actually use (TypeScript MCP SDK recommended; Python/FastMCP supported). Register anthropics/skills, install example-skills@anthropic-agent-skills, then trigger on MCP-server-building asks. Marketplace metadata version: 1.0.0 (catalog field; not per-skill semver). Checked 2026-09-24.
example-skills plugin (skill path ./skills/mcp-builder). Use when building or redesigning MCP tools for agents. Skip “just connect an existing MCP,” Office binaries (document-skills), Claude API apps without MCP design (claude-api radar), or doc co-writing (doc-coauthoring radar). [GAP]: no solo /plugin install mcp-builder@….What it does
SKILL.md frames quality as how well the server lets LLMs finish real tasks. Four phases:
- Deep research & planning: API coverage vs workflow tools; protocol docs via sitemap; plan endpoints; TypeScript recommended, Python/FastMCP supported.
- Implementation: project structure, API client, Zod/Pydantic schemas, tool annotations (
readOnlyHint,destructiveHint,idempotentHint,openWorldHint). - Review & test: build + MCP Inspector (
npx @modelcontextprotocol/inspector). - Evaluations: ten read-only, complex, verifiable QA pairs in XML.
Load-on-demand inside the skill: reference/mcp_best_practices.md, node_mcp_server.md, python_mcp_server.md, evaluation.md, plus a scripts/ folder. Folder contents same-day: SKILL.md, LICENSE.txt, reference/, scripts/.
Triggers: building MCP servers / integrating external APIs as tools (Python or Node/TypeScript).
When to use / when not
Use when you are greenfielding or redesigning MCP tools for agent workflows: naming, schemas, pagination, actionable errors, and an eval set.
Do not:
- Only need to add the marketplace / install a plugin → add anthropics/skills
- Primary deliverable is Office binaries →
document-skills(different plugin) - Claude API / SDK app code without MCP server design → live claude-api radar: do not re-Intake
- Structured doc co-writing → live doc-coauthoring radar: do not re-Intake
Install (Claude Code)
/plugin marketplace add anthropics/skills
Then Browse → anthropic-agent-skills → example-skills → Install, or direct:
/plugin install example-skills@anthropic-agent-skills
Fact (marketplace.json, 2026-09-24): plugin name is example-skills; skill path is ./skills/mcp-builder. Sibling skills in the same plugin include algorithmic-art, brand-guidelines, doc-coauthoring, skill-creator, and others: installing pulls the whole example set.
Walkthroughs: add the marketplace · sync Claude.ai skills / plugins · skill-doctor if load looks wrong.
Limits
- README disclaimer: skills are demo/reference; product behavior may differ
- Skill is a guide + reference library + scripts, not a hosted MCP generator
- Bundled with the full
example-skillsset: expect siblings, not a minimal single-skill package - Protocol/SDK URLs inside SKILL.md should be re-checked same-day if you quote them deeply
Pair with prior radars / guides
| Guide / radar | Moment |
|---|---|
| doc-coauthoring | Sibling example-skills radar: structured docs |
| claude-api | Claude API skill: not MCP server design |
| document-skills | xlsx / docx / pptx / pdf |
| add anthropics/skills marketplace | First /plugin setup |
| sync skills / plugins | Claude.ai ↔ Code |
| skill-doctor | Skill not loading |
Sources (checked 2026-09-24)
- marketplace.json: marketplace
anthropic-agent-skills; pluginexample-skills; skills include./skills/mcp-builder; metadata version 1.0.0 - SKILL.md: name, description, four phases, annotations, eval XML
- anthropics/skills README: marketplace add;
/plugin install example-skills@anthropic-agent-skills; demo/reference disclaimer - Skill tree: github.com/anthropics/skills/tree/main/skills/mcp-builder:
SKILL.md·LICENSE.txt·reference/·scripts/