Your agent calls an MCP tool that talks to an external API. Fifteen seconds pass. Thirty seconds. Then a cryptic 424 Failed Dependency error kills the whole workflow. The user sees nothing useful, your logs show nothing helpful. MCP tools are black boxes to the calling agent, so one slow API call cascades into full failure, and 300-second hangs burn resources with zero feedback. The async handleId pattern fixes it. start_long_job kicks off the operation and returns a job ID instantly. check_job_status lets the agent poll for results at controlled intervals while staying responsive. Failed or stalled jobs surface as clear error states. The talk builds a complete FastMCP server live, simulating four API behaviors: fast (2s), slow (15s), unresponsive (300s), and failing. You watch real 424 errors happen, then watch the pattern turn 300-second hangs into sub-4-second responses. You'll walk away with: • A FastMCP server implementing the async handleId pattern with job tracking • MCP debugging techniques for finding timeout root causes in production • Production job tracking with status management and cleanup • Client patterns for connecting agents to async MCP tools

Outline: • The 424 Problem • MCP Server Architecture • Async HandleId Pattern • Production Integration • Advanced Patterns and Wrap-Up