Patterns
Pattern 05 of 26
Model Context Protocol (MCP)
Write the tool once, use it everywhere
Before MCP, every agent application built its own integrations. You wanted your tool to work in Claude Code and also Cursor? Write it twice. MCP is the standard that changed that: one server, any compatible client. It is now under the Linux Foundation, which means it is no longer Anthropic's spec to change unilaterally. The ecosystem is real: 5,800+ community servers and 97 million monthly SDK downloads.
Why it matters
I use Claude Code daily and I connect MCP servers to it constantly. The productivity gain is not theoretical. You stop writing the same GitHub integration over and over and start actually building the thing you care about. That reduction in integration overhead is real money saved per agent project.
Deep Dive
Anthropic announced MCP in November 2024 to solve a specific, unglamorous problem: fragmentation. Every AI application was writing its own integrations, so the same Slack tool would need to be rebuilt for Claude, GPT, Gemini, and every other model that mattered. MCP defines a client-server protocol where the server exposes tools, resources, and prompts, and any MCP-compatible client can connect to it without modification. The idea is not novel in software. USB did the same thing for hardware peripherals decades ago. But it was missing in AI tooling.
In practice, you run an MCP server as a local process or a remote HTTP service. The client, which is your AI host application, connects to it and registers the server's tools alongside whatever native tools the model already has. The model then calls those tools using the same function-calling mechanism it uses for everything else. It does not know or care whether the tool is local or remote. The transport layer handles both stdio for local processes and HTTP with Server-Sent Events for remote ones. Setup is usually about twenty minutes the first time.
In December 2025 Anthropic donated MCP to the Linux Foundation's Agentic AI Foundation, alongside AGENTS.md. That matters more than it sounds. Vendor-controlled specs carry vendor risk. An industry foundation means the spec evolves through consensus, not through one company's roadmap decisions. By that point 5,800+ servers had been built on it. The failure mode worth knowing: MCP servers are only as reliable as their transport. Flaky stdio servers will silently drop tool calls. Build health checks into your server if you plan to run them in production.