CPU flamegraph
CPU Flamegraphs
Pinpoint main-thread blocking with interactive, frame-accurate flamegraphs.
System Investigator
WhySlow continuously investigates website performance, connects regressions to deployments and code changes, and shows you the evidence behind what made your website slower.
Split the checkout bundle and defer analytics — recover roughly 600 ms and bring checkout back to where it was.
Split the checkout bundle and defer analytics — recover roughly 600 ms and bring checkout back to where it was.
WhySlow surfaces the why behind every slowdown — from trace routes to the exact commit that introduced it.
Pinpoint main-thread blocking with interactive, frame-accurate flamegraphs.
See which requests are blocking others — and why.
Visualize layout thrashing hotspots instantly.
Automatically link performance regressions to the exact deployment and author responsible.
“WhySlow caught a regression before our users did. The trace route pointed straight to the culprit asset.”
“We recovered 400ms of LCP in a week because WhySlow showed us exactly which deploy broke it.”
“Finally a tool that explains the why, not just the what. Our page speed has never been more stable.”
The only way to know
Give WhySlow a URL and watch it reconstruct exactly what made your slowest page slow — the resource, the deploy, the commit. Free to start, no config.