tool-design-mcplisted

# Tool Design and MCP In 2026 the tool-integration question has a clear answer: **MCP by default**. The ecosystem now exceeds 10,000 active servers and 177,000 registered tools. Adoption by Anthropic, OpenAI, Google, and the broader community makes it the de facto standard. ## The two protocols **MCP (Model Context Protocol)** — agent ↔ tool - Anthropic, Nov 2024 - JSON-RPC 2.0 - Servers expose tools, resources, prompts - One server per integration; any MCP-aware client can use it **A2A (Agent2Agent)** — agent ↔ agent - Google, April 2025; donated to Linux Foundation June 2025 - Agents publish "Agent Cards" (capability metadata) - Tasks exchanged via HTTP/JSON They're **complementary, not competing.** MCP gives an agent its tools; A2A lets specialized agents delegate to each other across vendor boundaries. ## The NxM collapse Before MCP: every model × every tool = a custom integration. N × M problem. After MCP: one MCP server per tool, any MCP-aware client can consume it. N + M. **Practical implication:** if you write custom function-calling code for a tool that already has an MCP server, you're choosing technical debt. Search for an existing server first. ## Tool design as prompt engineering The single most important rule from Anthropic's "Building Effective Agents": **treat tool definitions like prompts**. Name them, describe them, give examples, document edge cases. Anthropic dedicates an appendix to "prompt-engineering your tools" for a reason. ### Required el