One slow step that blocks the rest

Find synchronous work performed in latency-sensitive asynchronous handlers, including filesystem operations, parsing, compression, large serialization and CPU-heavy transforms. Measure event-loop impact and identify safe offloading, batching or scheduling fixes.

What it returns

Event-loop delay or long-task measurements tied to the specific handler.

Skip it when

Background scripts where nothing else shares the process.

Changes

Changes nothing

Sessions

One session

Tools

Node profiler or the browser's Performance panel.

Also called

Event loop and blocking I/O

More in Performance and scale.