Agent Skills: MCP Expert

MCP Expert

[!IMPORTANT]

First Step: Read Project Config & MCP

Before making technical decisions, always check:

| File | Purpose | |------|---------| | project/CONFIG.yaml | Stack versions, modules, architecture | | mcp.yaml | Project MCP server config | | mcp/ | Project-specific MCP tools/resources |

Use project MCP server (named after project, e.g. mcp_<project-name>_*):

• list_resources → see available project data
• *_tools → project-specific actions (db, cache, jobs, etc.)

Use mcp_context7 for library docs:

• Check mcp.yaml → context7.default_libraries for pre-configured libs
• Example: libraryId: /nuxt/nuxt, query: "Nuxt 4 composables"

Expert-level guidance for building MCP servers. Primary language: Go (official SDK). Also covers Python and TypeScript.

When to Use This Skill

• Trigger: Create an MCP server or add tools/resources
• Trigger: Integrate a service via MCP (databases, APIs)
• Trigger: Debug MCP connection or transport issues
• Anti-pattern: Do NOT use for general API development without MCP context

Decision Tree

1. IF creating a new MCP server:

   • Use Go (primary) — see examples/go-server-official.go
   • Library: modelcontextprotocol/go-sdk (official, recommended)
   • Transport: stdio (IDE) or HTTP (web services)

2. IF adding to existing Go server:

   • Use s.AddTool() with handler function
   • Use s.AddResource() for read-only data

3. IF debugging:

   • Check mcp_config.json paths (must be absolute)
   • Use Inspector: npx @anthropic/mcp-inspector
   • Logs go to stderr (stdout reserved for JSON-RPC)

MCP Primitives

| Primitive | Purpose | Example | |-----------|---------|---------| | Tool | Execute actions with side effects | Run builds, create issues | | Resource | Expose read-only data | DB schemas, config files | | Prompt | Reusable prompt templates | Code review patterns |

Go Quick Reference (Official SDK)

server := mcp.NewServer(&mcp.Implementation{
    Name: "my-server", Version: "v1.0.0",
}, nil)

mcp.AddTool(server, &mcp.Tool{
    Name: "my_tool",
    Description: "Brief description",
}, HandleMyTool)

server.Run(ctx, &mcp.StdioTransport{})

Full example: See examples/go-server-official.go

Go Libraries

| Library | Install | Notes | |---------|---------|-------| | Official SDK | go get github.com/modelcontextprotocol/go-sdk | Recommended, Anthropic-maintained | | mark3labs/mcp-go | go get github.com/mark3labs/mcp-go | Alternative, good DX |

Antigravity Config (mcp_config.json)

{
  "mcpServers": {
    "my-server": {
      "command": "/absolute/path/to/server",
      "args": [],
      "env": { "API_KEY": "your-key" }
    }
  }
}

Key rules:

1. Always use absolute paths
2. Logs to stderr — stdout is for JSON-RPC only
3. Descriptions matter — LLM uses them for tool selection

Debugging Workflow

1. Check mcp_config.json paths
2. Test standalone: go run server.go
3. Use Inspector: npx @anthropic/mcp-inspector
4. Check stderr in terminal

Best Practices

Tool Design

• Use snake_case names: get_user, create_issue
• Write rich descriptions
• Validate inputs, return informative errors

Security

• Never log secrets to stdout/stderr
• Use environment variables for API keys

TDD Protocol (Hard Stop)

[!CAUTION] NO CODE WITHOUT FAILING TEST.

• Tools: Write a test that calls the tool with mock input -> Assert output.
• Resources: Write a test that reads the resource URI -> Assert content.

Agents MUST refuse to write implementation code if this loop is skipped.

Tech Debt Protocol (Hard Stop)

[!CAUTION] Follow ../standards/TECH_DEBT_PROTOCOL.md. When creating workarounds:

1. Add // TODO(TD-XXX): description in code
2. Register in project/docs/TECH_DEBT.md

Forbidden: Untracked TODOs, undocumented hardcoded values.

Git Protocol (Hard Stop)

[!CAUTION] Follow ../standards/GIT_PROTOCOL.md.

1. Branch: Work in feat/<name> or fix/<name>.
2. Commit: Use Conventional Commits (feat:, fix:).
3. Atomic: One commit = One logical change.

Reject: "wip", "update", "fix" as commit messages.

Team Collaboration

• Backend: @backend-go-expert (Integrates MCP into Go services)
• DevOps: @devops-sre (MCP server deployment, systemd units)
• CLI: @cli-architect (MCP tools for CLI applications)
• TMA: @tma-expert (MCP integration with Telegram Mini Apps)

When to Delegate

• ✅ Delegate to @backend-go-expert when: MCP server needs integration into larger Go service

• ✅ Delegate to @devops-sre when: MCP server ready for deployment

• ⬅️ Return to @systems-analyst if: Requirements unclear for tool design

Document Lifecycle

Protocol: DOCUMENT_STRUCTURE_PROTOCOL.md

| Operation | Document | Location | Trigger | |-----------|----------|----------|---------| | 🔵 Creates | server-config.md | active/mcp/ | MCP server design complete | | 📖 Reads | api-contracts.yaml | active/architecture/ | On activation | | 📝 Updates | ARTIFACT_REGISTRY.md | project/docs/ | On create, on complete | | 🟡 To Review | server-config.md | review/mcp/ | Ready for implementation | | ✅ Archive | — | closed/<work-unit>/ | @doc-janitor on final approval |

Pre-Handoff Validation (Hard Stop)

[!CAUTION] MANDATORY self-check before notify_user or delegation.

| # | Check | |---|-------| | 1 | ## Upstream Documents section exists with paths | | 2 | ## Requirements Checklist table exists | | 3 | All ❌ have explicit Reason: ... | | 4 | Document in review/ folder | | 5 | ARTIFACT_REGISTRY.md updated |

If ANY unchecked → DO NOT PROCEED.

Handoff Protocol

[!CAUTION] BEFORE handoff:

1. Save final document to project/docs/ path
2. Change file status from Draft to Approved in header/frontmatter
3. Update project/docs/ARTIFACT_REGISTRY.md status to ✅ Done
4. Use notify_user for final approval
5. THEN delegate to next skill

Examples

| File | Description | |------|-------------| | examples/go-server-official.go | Go server (official SDK) — recommended | | examples/go-server-mcp-go.go | Go server (mark3labs/mcp-go) — alternative | | examples/python-server.py | Python server (FastMCP) | | examples/typescript-server.ts | TypeScript server | | examples/mcp_config.json | Antigravity config |

Resources

• Docs: modelcontextprotocol.io
• Go (mcp-go): github.com/mark3labs/mcp-go
• Go (official): github.com/modelcontextprotocol/go-sdk
• Inspector: npx @anthropic/mcp-inspector