user: anonymous

{
  "path": "/blog/mcp",
  "attrs": {
    "date": "2025-03-10",
    "title": "Model Context Protocol (MCP)",
    "layout": "BlogPostLayout",
    "splash": {
      "image": "/images/courthouse.webp"
    }
  },
  "md": "# Model Context Protocol (MCP)\n\nMCP is a protocol for integrating AI applications with tools and external services. It was created by Anthropic as a way for [Claude](https://claude.ai/download) to access resources on the desktop, taking inspiration from [LSP](https://microsoft.github.io/language-server-protocol/) for editor extensions.\n\nMCP servers can be coded do almost anything, including network calls to other services. This has led to MCP being talked about as a foundation for building AI agents, even though the original desktop-centric transport is far from the Web protocols you might expect.\n\nWhat follows is very a quick overview of MCP. For deeper dives, I suggest:\n1. [How MCP was born](https://www.youtube.com/watch?v=m2VqaNKstGc) interview with [@dsp_](https://x.com/dsp_) and [@jspahrsummers](https://x.com/jspahrsummers) - April 3 '25\n2. [Workshop](https://www.youtube.com/watch?v=kQmXtrmQ5Zg) from the AI engineer summit - Feb '25\n3. MCP [User guide](https://modelcontextprotocol.io)\n4. MCP [Spec](https://spec.modelcontextprotocol.io/specification//2024-11-05/)\n5. MCP [TypeScript SDK](https://github.com/modelcontextprotocol/typescript-sdk)\n6. Example [MCP servers](https://github.com/modelcontextprotocol/servers)\n7. Swyx's [spicy take](https://www.latent.space/p/why-mcp-won)\n\n![MCP slide from the AI engineering summit https://www.youtube.com/watch?v=kQmXtrmQ5Zg](/images/mcp.webp)\n\n### How it works\n\nTo make a tool call, the [MCP client](https://modelcontextprotocol.io/clients) exchanges JSON-RPC messages with the [MCP server](https://modelcontextprotocol.io/examples).\n\nA desktop client will spawn servers as subprocesses so that it can communicate with them over [stdio](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio).\n\nBesides [tool calls](https://spec.modelcontextprotocol.io/specification/2024-11-05/server/tools/), the protocol also supports:\n\n- Server-to-client [notifications](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/messages/#notifications)\n- URL-based [resources](https://spec.modelcontextprotocol.io/specification/2024-11-05/server/resources/) with subscriptions for change notifications\n- Server-provided [Prompt templates](https://spec.modelcontextprotocol.io/specification/2024-11-05/server/prompts/)\n- Nested LLM calls or [sampling](https://spec.modelcontextprotocol.io/specification/2024-11-05/client/sampling/)\n\nThere are [debugging](https://modelcontextprotocol.io/docs/tools/debugging) tools and [SDKs](https://modelcontextprotocol.io/sdk) for Python, Typescript, Java, and Kotlin.\n\n### Why are people excited?\n\nTalking to your own tools feels like magic.\n\nUsing MCP, AI appplications (clients) can connect to tools (servers) without custom integration.\n\n![Screenshot of chat with Claude to inspect the local filesystem](/images/claude-magic.webp)\n\n[Here](https://www.youtube.com/watch?v=vGajZpl_9yA) is another example from Cloudflare.\n\n<iframe width=\"560\" height=\"315\" src=\"https://www.youtube.com/embed/vGajZpl_9yA?start=61\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen></iframe>\n\n### What's next?\nThe buzz is real, but it's early days and AI agent platforms are just getting started.\n\n- I'm optimistic for [HTTP](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse) to supplant stdio, especially with the [recent announcement](https://youtu.be/kQmXtrmQ5Zg?t=4409) of remote servers with auth.\n\n  This is particularly important for scaling agents on the network and supporting multiple clients per server.\n\n  _Update:_ See this [RFC](https://github.com/modelcontextprotocol/specification/pull/206) and [discussion](https://github.com/modelcontextprotocol/specification/discussions/102) for connectionless improvements to the HTTP transport. 🎉\n\n- A [registry](https://youtu.be/kQmXtrmQ5Zg?t=4920) should accelerate the network effects of MCP, making servers and their capabilities more discoverable e.g. by other agents.\n\n- [.well-known/mcp.json](https://youtu.be/kQmXtrmQ5Zg?t=5958) provides a way for agents to find AI interfaces on websites without the need for a central registry.\n\n- [Stateless requests, streaming, and namespacing](https://youtu.be/kQmXtrmQ5Zg?t=6095) - all good things adopted from Web protocols.\n\n### Growing pains\n\nThe way Claude Desktop spawns servers in subprocesses has resulted in a few [pitfalls](https://github.com/modelcontextprotocol/servers/issues/436#issuecomment-2564638983). I ran into this myself after configuring the filesystem server as described in the [quickstart](https://modelcontextprotocol.io/quickstart/user#2-add-the-filesystem-mcp-server).\n\n![Screenshot of Claude errors](/images/claude-errors.webp)\n\nThe error stems from differences in the PATH when Claude Desktop spawns server subprocesses. One fix is to use absolute paths in `~/Library/Application Support/Claude/claude_desktop_config.json` on MacOS. E.g.\n\n```json\n{\n  \"mcpServers\": {\n    \"filesystem\": {\n      \"command\": \"/Users/jldec/n/bin/node\",\n      \"args\": [\n        \"/Users/jldec/mcp/servers/src/filesystem/dist/index.js\",\n        \"/Users/jldec/mcp/claude\"\n      ]\n    }\n  }\n}\n```\n\n# 🚀",
  "html": "<h1>Model Context Protocol (MCP)</h1>\n<p>MCP is a protocol for integrating AI applications with tools and external services. It was created by Anthropic as a way for <a href=\"https://claude.ai/download\">Claude</a> to access resources on the desktop, taking inspiration from <a href=\"https://microsoft.github.io/language-server-protocol/\">LSP</a> for editor extensions.</p>\n<p>MCP servers can be coded do almost anything, including network calls to other services. This has led to MCP being talked about as a foundation for building AI agents, even though the original desktop-centric transport is far from the Web protocols you might expect.</p>\n<p>What follows is very a quick overview of MCP. For deeper dives, I suggest:</p>\n<ol>\n<li><a href=\"https://www.youtube.com/watch?v=m2VqaNKstGc\">How MCP was born</a> interview with <a href=\"https://x.com/dsp_\">@dsp_</a> and <a href=\"https://x.com/jspahrsummers\">@jspahrsummers</a> - April 3 '25</li>\n<li><a href=\"https://www.youtube.com/watch?v=kQmXtrmQ5Zg\">Workshop</a> from the AI engineer summit - Feb '25</li>\n<li>MCP <a href=\"https://modelcontextprotocol.io\">User guide</a></li>\n<li>MCP <a href=\"https://spec.modelcontextprotocol.io/specification//2024-11-05/\">Spec</a></li>\n<li>MCP <a href=\"https://github.com/modelcontextprotocol/typescript-sdk\">TypeScript SDK</a></li>\n<li>Example <a href=\"https://github.com/modelcontextprotocol/servers\">MCP servers</a></li>\n<li>Swyx's <a href=\"https://www.latent.space/p/why-mcp-won\">spicy take</a></li>\n</ol>\n<p><img src=\"/images/mcp.webp\" alt=\"MCP slide from the AI engineering summit https://www.youtube.com/watch?v=kQmXtrmQ5Zg\"></p>\n<h3>How it works</h3>\n<p>To make a tool call, the <a href=\"https://modelcontextprotocol.io/clients\">MCP client</a> exchanges JSON-RPC messages with the <a href=\"https://modelcontextprotocol.io/examples\">MCP server</a>.</p>\n<p>A desktop client will spawn servers as subprocesses so that it can communicate with them over <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio\">stdio</a>.</p>\n<p>Besides <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/server/tools/\">tool calls</a>, the protocol also supports:</p>\n<ul>\n<li>Server-to-client <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/messages/#notifications\">notifications</a></li>\n<li>URL-based <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/server/resources/\">resources</a> with subscriptions for change notifications</li>\n<li>Server-provided <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/server/prompts/\">Prompt templates</a></li>\n<li>Nested LLM calls or <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/client/sampling/\">sampling</a></li>\n</ul>\n<p>There are <a href=\"https://modelcontextprotocol.io/docs/tools/debugging\">debugging</a> tools and <a href=\"https://modelcontextprotocol.io/sdk\">SDKs</a> for Python, Typescript, Java, and Kotlin.</p>\n<h3>Why are people excited?</h3>\n<p>Talking to your own tools feels like magic.</p>\n<p>Using MCP, AI appplications (clients) can connect to tools (servers) without custom integration.</p>\n<p><img src=\"/images/claude-magic.webp\" alt=\"Screenshot of chat with Claude to inspect the local filesystem\"></p>\n<p><a href=\"https://www.youtube.com/watch?v=vGajZpl_9yA\">Here</a> is another example from Cloudflare.</p>\n<iframe width=\"560\" height=\"315\" src=\"https://www.youtube.com/embed/vGajZpl_9yA?start=61\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen></iframe>\n<h3>What's next?</h3>\n<p>The buzz is real, but it's early days and AI agent platforms are just getting started.</p>\n<ul>\n<li>\n<p>I'm optimistic for <a href=\"https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse\">HTTP</a> to supplant stdio, especially with the <a href=\"https://youtu.be/kQmXtrmQ5Zg?t=4409\">recent announcement</a> of remote servers with auth.</p>\n<p>This is particularly important for scaling agents on the network and supporting multiple clients per server.</p>\n<p><em>Update:</em> See this <a href=\"https://github.com/modelcontextprotocol/specification/pull/206\">RFC</a> and <a href=\"https://github.com/modelcontextprotocol/specification/discussions/102\">discussion</a> for connectionless improvements to the HTTP transport. 🎉</p>\n</li>\n<li>\n<p>A <a href=\"https://youtu.be/kQmXtrmQ5Zg?t=4920\">registry</a> should accelerate the network effects of MCP, making servers and their capabilities more discoverable e.g. by other agents.</p>\n</li>\n<li>\n<p><a href=\"https://youtu.be/kQmXtrmQ5Zg?t=5958\">.well-known/mcp.json</a> provides a way for agents to find AI interfaces on websites without the need for a central registry.</p>\n</li>\n<li>\n<p><a href=\"https://youtu.be/kQmXtrmQ5Zg?t=6095\">Stateless requests, streaming, and namespacing</a> - all good things adopted from Web protocols.</p>\n</li>\n</ul>\n<h3>Growing pains</h3>\n<p>The way Claude Desktop spawns servers in subprocesses has resulted in a few <a href=\"https://github.com/modelcontextprotocol/servers/issues/436#issuecomment-2564638983\">pitfalls</a>. I ran into this myself after configuring the filesystem server as described in the <a href=\"https://modelcontextprotocol.io/quickstart/user#2-add-the-filesystem-mcp-server\">quickstart</a>.</p>\n<p><img src=\"/images/claude-errors.webp\" alt=\"Screenshot of Claude errors\"></p>\n<p>The error stems from differences in the PATH when Claude Desktop spawns server subprocesses. One fix is to use absolute paths in <code>~/Library/Application Support/Claude/claude_desktop_config.json</code> on MacOS. E.g.</p>\n<pre><code class=\"language-json\">{\n  &quot;mcpServers&quot;: {\n    &quot;filesystem&quot;: {\n      &quot;command&quot;: &quot;/Users/jldec/n/bin/node&quot;,\n      &quot;args&quot;: [\n        &quot;/Users/jldec/mcp/servers/src/filesystem/dist/index.js&quot;,\n        &quot;/Users/jldec/mcp/claude&quot;\n      ]\n    }\n  }\n}\n</code></pre>\n<h1>🚀</h1>\n"
}