Windmill

Script Traps

• Main function signature determines input schema — Windmill infers from type hints, wrong types break the UI form
• Return value is the script output — forgetting to return means downstream steps get nothing
• Python dependencies go in inline requirements.txt comment — not a global file, each script is isolated
• TypeScript runs on Bun — Node.js-specific APIs may not work

Flow Execution

• results.step_name fails if step hasn't run yet — conditional branches cause undefined access errors
• Parallel branches need explicit configuration — default is sequential, not concurrent
• Suspend steps wait forever without timeout — set explicit timeout or flow hangs indefinitely
• Error handlers only catch step failures — script syntax errors bypass handlers

Scheduling Pitfalls

• Timezone defaults to server timezone — set explicitly or jobs fire at unexpected times
• Concurrent execution allowed by default — add mutex lock if jobs shouldn't overlap
• Schedules attach to scripts/flows — no standalone schedule entities, delete script = delete schedule