claude-plugins-official/plugins/mcp-server-dev/skills/build-mcp-server/SKILL.md

name, description, version

name	description	version
build-mcp-server	This skill should be used when the user asks to "build an MCP server", "create an MCP", "make an MCP integration", "wrap an API for Claude", "expose tools to Claude", "make an MCP app", or discusses building something with the Model Context Protocol. It is the entry point for MCP server development — it interrogates the user about their use case, determines the right deployment model (remote HTTP, MCPB, local stdio), picks a tool-design pattern, and hands off to specialized skills.	0.1.0

Build an MCP Server

You are guiding a developer through designing and building an MCP server that works seamlessly with Claude. MCP servers come in many forms — picking the wrong shape early causes painful rewrites later. Your first job is discovery, not code.

Do not start scaffolding until you have answers to the questions in Phase 1. If the user's opening message already answers them, acknowledge that and skip straight to the recommendation.

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Phase 1 — Interrogate the use case

Ask these questions conversationally (batch them into one message, don't interrogate one-at-a-time). Adapt wording to what the user has already told you.

1. What does it connect to?

If it connects to…	Likely direction
A cloud API (SaaS, REST, GraphQL)	Remote HTTP server
A local process, filesystem, or desktop app	MCPB or local stdio
Hardware, OS-level APIs, or user-specific state	MCPB
Nothing external — pure logic / computation	Either — default to remote

2. Who will use it?

• Just me / my team, on our machines → Local stdio is acceptable (easiest to prototype)
• Anyone who installs it → Remote HTTP (strongly preferred) or MCPB (if it must be local)
• Users of Claude desktop who want UI widgets → MCP app (remote or MCPB)

3. How many distinct actions does it expose?

This determines the tool-design pattern — see Phase 3.

• Under ~15 actions → one tool per action
• Dozens to hundreds of actions (e.g. wrapping a large API surface) → search + execute pattern

4. Does it need interactive UI in the chat?

Forms, pickers, dashboards, confirmation dialogs rendered inline in the conversation → MCP app (adds UI resources on top of a standard server).

5. What auth does the upstream service use?

• None / API key → straightforward
• OAuth 2.0 → you'll need a remote server with DCR (Dynamic Client Registration) or CIMD support; see references/auth.md

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Phase 2 — Recommend a deployment model

Based on the answers, recommend one path. Be opinionated. The ranked options:

⭐ Remote streamable-HTTP MCP server (default recommendation)

A hosted service speaking MCP over streamable HTTP. This is the recommended path for anything wrapping a cloud API.

Why it wins:

• Zero install friction — users add a URL, done
• One deployment serves all users; you control upgrades
• OAuth flows work properly (the server can handle redirects, DCR, token storage)
• Works across Claude desktop, Claude Code, Claude.ai, and third-party MCP hosts

Choose this unless the server must touch the user's local machine.

→ Scaffold with references/remote-http-scaffold.md

MCP app (remote HTTP + interactive UI)

Same as above, plus UI resources — interactive widgets rendered in chat. Forms, file pickers, rich previews, confirmation dialogs. Built once, renders in Claude and ChatGPT.

Choose this when one or more tools benefit from structured user input or rich output that plain text can't handle.

Usually remote, but can be shipped as MCPB if the UI needs to drive a local app.

→ Hand off to the build-mcp-app skill.

MCPB (bundled local server)

A local MCP server packaged with its runtime so users don't need Node/Python installed. The sanctioned way to ship local servers.

Choose this when the server must run on the user's machine — it reads local files, drives a desktop app, talks to localhost services, or needs OS-level access.

→ Hand off to the build-mcpb skill.

Local stdio (npx / uvx) — not recommended for distribution

A script launched via npx / uvx on the user's machine. Fine for personal tools and prototypes. Painful to distribute: users need the right runtime, you can't push updates, and the only distribution channel is Claude Code plugins.

Recommend this only as a stepping stone. If the user insists, scaffold it but note the MCPB upgrade path.

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Phase 3 — Pick a tool-design pattern

Every MCP server exposes tools. How you carve them matters more than most people expect — tool schemas land directly in Claude's context window.

Pattern A: One tool per action (small surface)

When the action space is small (< ~15 operations), give each a dedicated tool with a tight description and schema.

create_issue    — Create a new issue. Params: title, body, labels[]
update_issue    — Update an existing issue. Params: id, title?, body?, state?
search_issues   — Search issues by query string. Params: query, limit?
add_comment     — Add a comment to an issue. Params: issue_id, body

Why it works: Claude reads the tool list once and knows exactly what's possible. No discovery round-trips. Each tool's schema validates inputs precisely.

Especially good when one or more tools ship an interactive widget (MCP app) — each widget binds naturally to one tool.

Pattern B: Search + execute (large surface)

When wrapping a large API (dozens to hundreds of endpoints), listing every operation as a tool floods the context window and degrades model performance. Instead, expose two tools:

search_actions  — Given a natural-language intent, return matching actions
                  with their IDs, descriptions, and parameter schemas.
execute_action  — Run an action by ID with a params object.

The server holds the full catalog internally. Claude searches, picks, executes. Context stays lean.

Hybrid: Promote the 3–5 most-used actions to dedicated tools, keep the long tail behind search/execute.

→ See references/tool-design.md for schema examples and description-writing guidance.

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Phase 4 — Pick a framework

Recommend one of these two. Others exist but these have the best MCP-spec coverage and Claude compatibility.

Framework	Language	Use when
Official TypeScript SDK (@modelcontextprotocol/sdk)	TS/JS	Default choice. Best spec coverage, first to get new features.
FastMCP 2.0	Python	User prefers Python, or wrapping a Python library. Decorator-based, very low boilerplate.

If the user already has a language/stack in mind, go with it — both produce identical wire protocol.

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Phase 5 — Scaffold and hand off

Once you've settled the four decisions (deployment model, tool pattern, framework, auth), do one of:

1. Remote HTTP, no UI → Scaffold inline using references/remote-http-scaffold.md. This skill can finish the job.
2. MCP app (UI widgets) → Summarize the decisions so far, then load the build-mcp-app skill.
3. MCPB (bundled local) → Summarize the decisions so far, then load the build-mcpb skill.
4. Local stdio prototype → Scaffold inline (simplest case), flag the MCPB upgrade path.

When handing off, restate the design brief in one paragraph so the next skill doesn't re-ask.

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Quick reference: decision matrix

Scenario	Deployment	Tool pattern
Wrap a small SaaS API	Remote HTTP	One-per-action
Wrap a large SaaS API (50+ endpoints)	Remote HTTP	Search + execute
SaaS API with rich forms / pickers	MCP app (remote)	One-per-action
Drive a local desktop app	MCPB	One-per-action
Local desktop app with in-chat UI	MCP app (MCPB)	One-per-action
Read/write local filesystem	MCPB	Depends on surface
Personal prototype	Local stdio	Whatever's fastest

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Reference files

• references/remote-http-scaffold.md — minimal remote server in TS SDK and FastMCP
• references/tool-design.md — writing tool descriptions and schemas Claude understands well
• references/auth.md — OAuth, DCR, CIMD, token storage patterns