Mcp builder

Skill nguyenthdat/opencode-starter/skills/mcp-builder

Opinionated OpenCode configuration with reusable agents, document skills, MCP integrations, custom tooling, and cross-platform workstation bootstrap.

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npx -y skills add nguyenthdat/opencode-starter --skill mcp-builder

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Guide for creating high-quality MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. Use when building MCP servers to integrate external APIs or services in any official SDK language: Python (FastMCP), TypeScript/Node, Go, Rust (rmcp), Java, Kotlin, C#/.NET, PHP, Ruby, or Swift.

SKILL.md

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MCP Server Development Guide

Overview

Create MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. The quality of an MCP server is measured by how well it enables LLMs to accomplish real-world tasks.

Process

🚀 High-Level Workflow

Creating a high-quality MCP server involves four main phases:

Phase 1: Deep Research and Planning

1.1 Understand Modern MCP Design

API Coverage vs. Workflow Tools: Balance comprehensive API endpoint coverage with specialized workflow tools. Workflow tools can be more convenient for specific tasks, while comprehensive coverage gives agents flexibility to compose operations. Performance varies by client—some clients benefit from code execution that combines basic tools, while others work better with higher-level workflows. When uncertain, prioritize comprehensive API coverage.

Tool Naming and Discoverability: Clear, descriptive tool names help agents find the right tools quickly. Use consistent prefixes (e.g., github_create_issue, github_list_repos) and action-oriented naming.

Context Management: Agents benefit from concise tool descriptions and the ability to filter/paginate results. Design tools that return focused, relevant data. Some clients support code execution which can help agents filter and process data efficiently.

Actionable Error Messages: Error messages should guide agents toward solutions with specific suggestions and next steps.

1.2 Study MCP Protocol Documentation

Navigate the MCP specification:

Start with the sitemap to find relevant pages: https://modelcontextprotocol.io/sitemap.xml

Then fetch specific pages with .md suffix for markdown format (e.g., https://modelcontextprotocol.io/specification/draft.md).

Key pages to review:

Specification overview and architecture
Transport mechanisms (streamable HTTP, stdio)
Tool, resource, and prompt definitions

1.3 Study Framework Documentation

Recommended stack:

Language: TypeScript (high-quality SDK support and good compatibility in many execution environments e.g. MCPB. Plus AI models are good at generating TypeScript code, benefiting from its broad usage, static typing and good linting tools). All ten official SDK languages are supported below—pick the one that matches the target service and runtime.
Transport: Streamable HTTP for remote servers, using stateless JSON (simpler to scale and maintain, as opposed to stateful sessions and streaming responses). stdio for local servers.

Load framework documentation:

MCP Best Practices: 📋 View Best Practices - Core guidelines

For TypeScript (recommended):

TypeScript SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/README.md
⚡ TypeScript Guide - TypeScript patterns and examples

For Python:

Python SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/python-sdk/main/README.md
🐍 Python Guide - Python patterns and examples

For Go:

Go SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/go-sdk/main/README.md
🐹 Go Guide - Go patterns and examples

For Rust:

Rust SDK (rmcp): Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/rust-sdk/main/README.md
🦀 Rust Guide - Rust patterns and examples

For Java:

Java SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/java-sdk/main/README.md (server guide: https://java.sdk.modelcontextprotocol.io/latest/server/)
☕ Java Guide - Java patterns and examples

For Kotlin:

Kotlin SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/kotlin-sdk/main/README.md
🟪 Kotlin Guide - Kotlin patterns and examples

For C# / .NET:

C# SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/csharp-sdk/main/README.md (getting started: https://csharp.sdk.modelcontextprotocol.io/concepts/getting-started.html)
🔷 C# Guide - C#/.NET patterns and examples

For PHP:

PHP SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/php-sdk/main/README.md
🐘 PHP Guide - PHP patterns and examples

For Ruby:

Ruby SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/ruby-sdk/main/README.md
💎 Ruby Guide - Ruby patterns and examples

For Swift:

Swift SDK: Use WebFetch to load https://raw.githubusercontent.com/modelcontextprotocol/swift-sdk/main/README.md
🐦 Swift Guide - Swift patterns and examples

1.4 Plan Your Implementation

Understand the API: Review the service's API documentation to identify key endpoints, authentication requirements, and data models. Use web search and WebFetch as needed.

Tool Selection: Prioritize comprehensive API coverage. List endpoints to implement, starting with the most common operations.

Phase 2: Implementation

2.1 Set Up Project Structure

See language-specific guides for project setup:

⚡ TypeScript Guide - Project structure, package.json, tsconfig.json
🐍 Python Guide - Module organization, dependencies
🐹 Go Guide - Module layout, go.mod, struct-tag schemas
🦀 Rust Guide - Crate structure, Cargo.toml, feature flags
☕ Java Guide - Maven/Gradle + BOM, McpServer builder
🟪 Kotlin Guide - Gradle setup, Ktor engine, coroutines
🔷 C# Guide - NuGet packages, generic host, DI
🐘 PHP Guide - Composer, PSR-4, attribute discovery
💎 Ruby Guide - Gemfile, tool classes, transports
🐦 Swift Guide - SwiftPM, method handlers, async/await

2.2 Implement Core Infrastructure

Create shared utilities:

API client with authentication
Error handling helpers
Response formatting (JSON/Markdown)
Pagination support

2.3 Implement Tools

For each tool:

Input Schema:

Use the SDK's idiomatic schema mechanism: Zod (TypeScript), Pydantic (Python), serde + schemars (Rust), struct tags (Go), or JSON Schema / attributes / typed parameters (Java, Kotlin, C#, PHP, Ruby, Swift)
Include constraints and clear descriptions
Add examples in field descriptions

Output Schema:

Define outputSchema where possible for structured data
Use structuredContent in tool responses (TypeScript SDK feature; in Rust return Json<T> to auto-generate the output schema; in Go return a typed output struct; in Java/C#/Ruby define an output schema / return typed objects)
Helps clients understand and process tool outputs

Tool Description:

Concise summary of functionality
Parameter descriptions
Return type schema

Implementation:

Async/await for I/O operations
Proper error handling with actionable messages
Support pagination where applicable
Return both text content and structured data when using modern SDKs

Annotations:

readOnlyHint: true/false
destructiveHint: true/false
idempotentHint: true/false
openWorldHint: true/false

Phase 3: Review and Test

3.1 Code Quality

Review for:

No duplicated code (DRY principle)
Consistent error handling
Full type coverage
Clear tool descriptions

3.2 Build and Test

TypeScript:

Run npm run build to verify compilation
Test with MCP Inspector: npx @modelcontextprotocol/inspector

Python:

Verify syntax: uv run python -m py_compile your_server.py
Test with MCP Inspector

Go:

Verify build: go build ./... (and go vet ./...)
Test with MCP Inspector

Rust:

Verify compilation: cargo check (and lint with cargo clippy)
Test with MCP Inspector

Java:

Build a runnable jar: ./mvnw package (or ./gradlew shadowJar)
Test with MCP Inspector

Kotlin:

Build/run: ./gradlew run (or installDist)
Test with MCP Inspector

C# / .NET:

Verify build: dotnet build
Test with MCP Inspector

PHP:

Install deps: composer install; run php bin/server.php
Test with MCP Inspector

Ruby:

Install deps: bundle install; run ruby bin/server.rb
Test with MCP Inspector

Swift:

Verify build: swift build
Test with MCP Inspector

See language-specific guides for detailed testing approaches and quality checklists.

Phase 4: Create Evaluations

After implementing your MCP server, create comprehensive evaluations to test its effectiveness.

Load ✅ Evaluation Guide for complete evaluation guidelines.

4.1 Understand Evaluation Purpose

Use evaluations to test whether LLMs can effectively use your MCP server to answer realistic, complex questions.

4.2 Create 10 Evaluation Questions

To create effective evaluations, follow the process outlined in the evaluation guide:

Tool Inspection: List available tools and understand their capabilities
Content Exploration: Use READ-ONLY operations to explore available data
Question Generation: Create 10 complex, realistic questions
Answer Verification: Solve each question yourself to verify answers

4.3 Evaluation Requirements

Ensure each question is:

Independent: Not dependent on other questions
Read-only: Only non-destructive operations required
Complex: Requiring multiple tool calls and deep exploration
Realistic: Based on real use cases humans would care about
Verifiable: Single, clear answer that can be verified by string comparison
Stable: Answer won't change over time

4.4 Output Format

Create an XML file with this structure:

<evaluation>
  <qa_pair>
    <question>Find discussions about AI model launches with animal codenames. One model needed a specific safety designation that uses the format ASL-X. What number X was being determined for the model named after a spotted wild cat?</question>
    <answer>3</answer>
  </qa_pair>
<!-- More qa_pairs... -->
</evaluation>

Reference Files

📚 Documentation Library

Load these resources as needed during development:

Core MCP Documentation (Load First)

MCP Protocol: Start with sitemap at https://modelcontextprotocol.io/sitemap.xml, then fetch specific pages with .md suffix
📋 MCP Best Practices - Universal MCP guidelines including:
- Server and tool naming conventions
- Response format guidelines (JSON vs Markdown)
- Pagination best practices
- Transport selection (streamable HTTP vs stdio)
- Security and error handling standards

SDK Documentation (Load During Phase 1/2)

Fetch the README for the language you are targeting:

Python SDK: https://raw.githubusercontent.com/modelcontextprotocol/python-sdk/main/README.md
TypeScript SDK: https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/README.md
Go SDK: https://raw.githubusercontent.com/modelcontextprotocol/go-sdk/main/README.md
Rust SDK (rmcp): https://raw.githubusercontent.com/modelcontextprotocol/rust-sdk/main/README.md
Java SDK: https://raw.githubusercontent.com/modelcontextprotocol/java-sdk/main/README.md
Kotlin SDK: https://raw.githubusercontent.com/modelcontextprotocol/kotlin-sdk/main/README.md
C# SDK: https://raw.githubusercontent.com/modelcontextprotocol/csharp-sdk/main/README.md
PHP SDK: https://raw.githubusercontent.com/modelcontextprotocol/php-sdk/main/README.md
Ruby SDK: https://raw.githubusercontent.com/modelcontextprotocol/ruby-sdk/main/README.md
Swift SDK: https://raw.githubusercontent.com/modelcontextprotocol/swift-sdk/main/README.md

Language-Specific Implementation Guides (Load During Phase 2)

Each guide covers server initialization, tool registration, input/output schemas, error handling, transports, a complete working example, and a quality checklist.

🐍 Python Implementation Guide - FastMCP, @mcp.tool, Pydantic
⚡ TypeScript Implementation Guide - server.registerTool, Zod
🐹 Go Implementation Guide - mcp.NewServer / mcp.AddTool, struct-tag schemas
🦀 Rust Implementation Guide - #[tool] / #[tool_router], serde + schemars
☕ Java Implementation Guide - McpServer.sync, SyncToolSpecification, two-tier errors
🟪 Kotlin Implementation Guide - Server.addTool, Ktor mcpStreamableHttp, coroutines
🔷 C# Implementation Guide - [McpServerTool], WithToolsFromAssembly, DI
🐘 PHP Implementation Guide - #[McpTool], Server::builder, discovery
💎 Ruby Implementation Guide - MCP::Tool subclasses, MCP::Server
🐦 Swift Implementation Guide - Server, withMethodHandler(CallTool.self), async/await

Evaluation Guide (Load During Phase 4)

✅ Evaluation Guide - Complete evaluation creation guide with:
- Question creation guidelines
- Answer verification strategies
- XML format specifications
- Example questions and answers
- Running an evaluation with the provided scripts