Model Context Protocol - Tools

Type: official-doc Tier: 1 (Official Doc) Author(s): Model Context Protocol Date: 2025-06-18 URL: https://modelcontextprotocol.io/specification/2025-06-18/server/tools Accessed: 2026-06-02

Why This Source Matters

This is the primary source for MCP tools. It connects directly to Projects 06 and 08: the learner already knows tool definitions inside one app loop; MCP tools show how those definitions become discoverable and callable across a protocol boundary.

Key Claims

• MCP tools are model-controlled capabilities that servers expose for language models to invoke.
• A tool definition includes a unique name, optional title, human-readable description, inputSchema, optional outputSchema, and optional annotations.
• Clients discover tools with tools/list and invoke tools with tools/call.
• Tool results can include unstructured content, structuredContent, resource links, or embedded resources.
• Tool errors are separated into protocol errors and tool execution errors; execution errors can be returned with isError: true.
• Servers must validate tool inputs, implement access controls, rate limit invocations, and sanitize outputs.
• Clients should show tool inputs, request confirmation for sensitive operations, validate results, set timeouts, and log usage.

Relevant To

• concepts: [mcp-tools, tool-schema, structured-output, tool-result, tool-security, provider-consumer-split]
• projects: [06-ai-coding-copilot, 08-ai-agent, 09-personal-learning-os, elective-mcp-interface-layer]

Notes

MCP tools should not be taught as "more function calling." The useful distinction is that the tool provider is now decoupled from the host that consumes it.