Merge pull request modelcontextprotocol#888 from projectAcetylcholine/mcp-logging-best-practices

docs: Update server.mdx to including MCP server logging best practices

Author: dsp-ant

docs/quickstart/server.mdx

@@ -46,6 +46,41 @@ This quickstart assumes you have familiarity with:
 - Python
 - LLMs like Claude
 
+### Logging in MCP Servers
+
+When implementing MCP servers, be careful about how you handle logging:
+
+**For STDIO-based servers:** Never write to standard output (stdout). This includes:
+
+- `print()` statements in Python
+- `console.log()` in JavaScript
+- `fmt.Println()` in Go
+- Similar stdout functions in other languages
+
+Writing to stdout will corrupt the JSON-RPC messages and break your server.
+
+**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
+
+### Best Practices
+
+1. Use a logging library that writes to stderr or files, such as `logging` in Python.
+2. For JavaScript, be especially careful - `console.log()` writes to stdout by default
+
+### Quick Examples
+
+````javascript
+// ❌ Bad (STDIO)
+console.log("Server started");
+
+// ✅ Good (STDIO)
+console.error("Server started");  // stderr is safe
+```python
+# ❌ Bad (STDIO)
+print("Processing request")
+
+# ✅ Good (STDIO)
+import logging
+logging.info("Processing request")
 ### System requirements
 
 - Python 3.10 or higher installed.