Metrics
Route Load
The loading time of an in-app navigation in a single-page app, where no full page reload happens.
In a single-page application, clicking a link swaps content client-side instead of loading a fresh document, so the classic load event never fires again. Route Load measures those soft navigations: how long a view change takes from click to painted content.
Without it, SPAs look artificially fast because only the very first load is measured. fastmon detects soft navigations and times each route change so the numbers reflect what visitors actually wait for.
Related terms
- CWVCore Web VitalsGoogle's set of three field metrics for loading (LCP), interactivity (INP) and visual stability (CLS) of a page.
- LCPLargest Contentful PaintThe time until the largest visible element in the viewport (image, video or text block) has rendered.
- INPInteraction to Next PaintHow long the page takes to visually respond after a user interacts, measured across the whole visit.
- CLSCumulative Layout ShiftA unitless score for how much visible content unexpectedly moves around while the page loads and runs.
- FCPFirst Contentful PaintThe moment the browser renders the first piece of content: text, an image or a canvas.
- TTFBTime to First ByteThe time from the start of navigation until the browser receives the first byte of the response.
- FIDFirst Input Delay (retired)The delay between a visitor's first interaction and the browser starting to process it. Replaced by INP.
- TBTTotal Blocking TimeThe total time the main thread was blocked by long tasks between first paint and interactivity, measured in the lab.
- SISpeed IndexA lab metric for how quickly the visible parts of a page fill in during load, based on video capture.
- TTITime to Interactive (legacy)A lab metric for when a page has rendered and can reliably respond to input quickly.
- Page LoadThe classic load event: everything on the initial page, including images and subresources, has finished loading.
- Long Tasks & LoAFAny piece of JavaScript that occupies the main thread for more than 50 ms, blocking the page from responding.
- Experience ScoreA single 0 to 10 number fastmon derives from LCP, INP, CLS, FCP, TTFB, load time and error rate.
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