Build an MCP Server

This chapter uses a documentation search server as a design example. You can implement it with any MCP SDK; the tutorial focuses on interface shape and quality criteria.

Capability definition

Goal: let an agent search tutorial pages and receive a few high-quality candidate links.

{
  "name": "search_docs",
  "description": "Search tutorial pages by keyword.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "query": { "type": "string" },
      "limit": { "type": "number", "default": 5 }
    },
    "required": ["query"]
  }
}

Response

{
  "results": [
    {
      "title": "MCP Introduction",
      "url": "/en/guide/mcp/",
      "summary": "Explains MCP responsibilities and a minimal design flow.",
      "score": 0.92
    }
  ]
}

Harness scenarios

Scenario	Input	Expected
Normal search	{"query":"MCP"}	Related pages, no more than limit
Empty query	{"query":""}	Structured error
No results	{"query":"unknown-term"}	Empty array and next-step hint
Excessive limit	{"query":"Skill","limit":1000}	Limit is capped

Implementation checklist

• Stable tool name.
• Input and output schemas.
• Agent-readable errors.
• No secrets in logs.
• Harness covers success and failure.
• Docs include sample request and response.

Next: MCP Practice.