Tag See all →

#mcp

1 stories

Banner: MCP stdio server breaks because log lines are mixed into the JSON-RPC stream on stdout

AI & Machine Learning Bug Report

MCP server disconnects over stdio: print statements corrupt JSON-RPC

Ryan Pham · May 15, 2025 · 7 min read

Our internal MCP server passed every test in the inspector but kept failing in the desktop client with an 'is not valid JSON' error. A startup banner and a debug print went to stdout, which is the protocol channel in stdio transport. Logging to stderr fixed it.