Use Puppeteer tracing to record the browser work around a repeatable slow page load or interaction, then inspect the trace in Chrome DevTools’ Performance panel. Start tracing before the relevant navigation or action, stop as soon as the interval is captured, and use the trace to form a testable hypothesis—not as a standalone measure of real-user speed.
Choose the right recording: page load or runtime
First pin down when the slowness happens. If it occurs while navigating and loading the page, capture a load recording. If the page is already open and a click, typing, scrolling, or other behavior is slow, capture the runtime interval caused by that interaction. Chrome DevTools distinguishes these recording types and recommends recording an issue that you can reproduce consistently: Performance recording guidance.
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Keep the URL, browser conditions, test data, and sequence of actions as consistent as practical between recordings. A repeatable capture makes it easier to tell whether a code change affected the work visible in the trace.
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The core API is page.tracing.start() followed by page.tracing.stop(). Start immediately before the navigation or interaction you want to inspect, then stop after the relevant interval. Puppeteer’s tracing example uses this start, navigate, stop pattern: Tracing class.
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Runnable navigation example
Save this as trace-page.js in a project with Puppeteer installed, then run node trace-page.js. It writes the browser trace to trace.json in the current directory.
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.tracing.start({ path: 'trace.json' });
await page.goto('https://example.com', { waitUntil: 'load' });
await page.tracing.stop();
} finally {
await browser.close();
}
})();For an interaction issue, load the page before starting the trace so the capture focuses on runtime work:
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await page.goto('https://example.com', { waitUntil: 'load' });
await page.tracing.start({ path: 'interaction-trace.json' });
await page.click('#slow-control');
await page.tracing.stop();Replace #slow-control with a selector for the action you are investigating. If the behavior requires several steps, keep only the relevant steps between start and stop; an unnecessarily long capture can make the interval harder to inspect.
Tracing options
Puppeteer documents these tracing options in its TracingOptions interface:
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pathwrites the trace to a file. If you omit it,tracing.stop()can return the trace as aUint8Arrayinstead.categoriescontrols which trace categories are included; prefix a category with-to exclude it. Leave categories at their defaults unless you have a reason to narrow or expand the recording.screenshotscontrols screenshot capture and defaults tofalse.bufferSizeconfigures the trace buffer. Puppeteer documents a default of 200 MB (200,000 KB) when the option is omitted or set to zero; this is a buffer setting, not a performance benchmark.
Only one trace can be active at a time per browser, so do not start overlapping traces on pages in the same browser instance.
Open and read the trace in Chrome DevTools
- Open Chrome DevTools and select the Performance panel.
- Open the saved
trace.jsontrace in the panel. Chrome documents saving and sharing trace files in its trace guide. - Zoom into the interval where the slowness occurred. Inspect main-thread activity and relevant performance markers around the navigation or interaction.
- Use the analysis view that answers your question: Call tree for root activities with substantial work, Bottom-up for activities that consume time directly, or Event log to follow events in sequence.
- Compare Self Time with Total Time for an activity. Self Time is work performed directly in that activity; Total Time includes its children. A large Total Time alongside smaller Self Time points you toward work in descendants, while high Self Time makes the activity itself a stronger lead.
Chrome describes these Performance panel views and timing fields in its Performance features reference.
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Which view should you use?
| View | Best for | What to look for |
|---|---|---|
| Call tree | Finding root activities associated with substantial work | Expand a costly parent activity to see the work beneath it. |
| Bottom-up | Finding direct time sinks | Look for activities with substantial Self Time. |
| Event log | Understanding sequence | Follow event order through the recorded interval. |
These are different ways to examine the same recording, not competing tracing tools. Use more than one view when you need both a likely source and the order in which the browser reached it.
Turn a trace into a useful diagnosis
A trace shows where recorded time went; it does not, by itself, prove the underlying cause or establish representative real-user performance. Treat a costly activity as a diagnostic lead. Form a specific hypothesis, change one likely cause, and record again under the same conditions. If the activity or interval changes as expected, that strengthens the hypothesis; if not, inspect another part of the trace.
Keep trace duration separate from a clean speed measurement. Tracing instruments browser work, and Chrome warns that advanced paint instrumentation is slow and significantly hinders performance. Do not use a heavily instrumented trace as an end-user timing result: Chrome Performance features reference.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common problems and fixes
- The trace file is missing or empty: Confirm that
page.tracing.start()completed before the work and thatpage.tracing.stop()ran afterward. Check that the process can write to the directory named bypath. - The capture contains the wrong activity: For a runtime issue, finish navigation before starting the trace. For a load issue, start tracing before navigation. Keep the capture interval tightly focused on the work of interest.
- Puppeteer reports that tracing is already active: A browser can have only one active trace at a time. Stop the active trace before starting another.
- The event of interest is difficult to find: Reproduce the issue consistently, narrow the capture window, and zoom into that interval in the Performance panel. Use Event log to establish sequence, then Call tree or Bottom-up to inspect work.
- The trace seems to slow the page: Remember that tracing adds instrumentation. Avoid advanced paint instrumentation unless you specifically need it, and do not treat trace timing as a representative user speed result.
Handle trace files as sensitive data
Review a trace before sharing it. Chrome says exported traces can include script content and source maps; in some circumstances, user-specific script content injected by a server could contain secrets. Puppeteer also warns that protocol logs may include sensitive information. Share diagnostic artifacts only with people who should see their contents: Puppeteer debugging guidance and Chrome trace sharing guidance.
Or skip the browser setup
If you need a screenshot rather than a browser performance trace, ScreenshotNeo provides a one-call screenshot API. It is not a substitute for Puppeteer tracing or DevTools’ timing analysis.
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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpScreenshotNeo removes cookie banners, newsletter popups, and chat widgets before the screenshot; bot checks, blank pages, and failed loads are never billed. Its MCP server lets AI agents take screenshots. The Free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000. The service is at ScreenshotNeo.
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