stdio vs HTTP MCP Servers

How Each Type Works

• **stdio (standard I/O)**
  • › AI spawns a process and communicates via stdin/stdout
  • › New process per session means clean state every time
  • › Best for heavy tools needing isolation (AEM, Playwright)
  • › No port conflicts, but has startup time on first use
• **HTTP (always running)**
  • › Server runs continuously, AI sends HTTP requests
  • › Always running means instant responses
  • › Best for lightweight services (Figma desktop app)
  • › Fast and shared across sessions, but must be running before you start
• **Config format difference**
  • › stdio uses 'command' and 'args' fields
  • › HTTP uses 'type: http' and 'url' fields pointing to the running endpoint

When to Use Which

1. 1 **Decision guide**
   • › Needs browser/process access? → stdio
   • › Desktop app exposing an API? → HTTP
   • › Need fresh state per session? → stdio
   • › Need shared state across sessions? → HTTP
   • › Worried about port conflicts? → stdio
2. 2 **stdio config example**
   • › "command": "npx", "args": ["aem-mcp-server", "-t", "stdio"]
3. 3 **HTTP config example**
   • › "type": "http", "url": "http://127.0.0.1:3845/mcp"
4. 4 **Check your .mcp.json** — Identify which of your servers are stdio vs HTTP and whether the choice matches the decision guide above