Tested 2026-07-28 02:43:03 using Chrome 150.0.7871.186 (script).(runtime settings)
Test as a logged in userLogin the user with an empty browser cache, then visit Obama and Facebook
The red band on the timeline marks when the main thread was busy with long tasks: moments when the page could not paint or respond, however the video looks.
Download videoUse --filmstrip.showAll to show all filmstrips.
Click a frame to seek the video to that moment. The dot marks frames where the page changed visually.
The whole recording in one image: every pixel is tinted by how often it changed. Amber changed once, deep red changed ten or more times. The scale is fixed, so heatmaps from different runs compare directly.
Flat amber is a page that painted once and stayed put. Red speckle in the shape of the text means the same pixels repainted over and over, usually invisible rendering noise that inflates Last Visual Change and Speed Index. A solid red block is a genuinely restless area, like an ad or a carousel.
How smoothly Chrome delivered frames to the screen during the test. Dropped counts only frames Chrome flags as affecting smoothness. On mostly-static pages the longest gap includes idle time where there was simply nothing to draw.
The server dominated the wait. The first byte took 1.819 s (72 % of the time to First Contentful Paint). Nothing can render before it arrives, and Google Web Vitals considers a TTFB over 800 ms in need of improvement. See the request timing on the Waterfall tab. First paint landed at 2.520 s; the 4 render-blocking requests were done by 2.363 s and the remaining ~157 ms is style and layout work (45 ms of it measured style recalculation).
Style the browser had to recalculate before it could paint: many elements or a lot of time spent here points at expensive CSS on the critical rendering path. The recalculation count and the largest single one tell the two problems apart: one massive style change touching most of the page (few recalculations, the largest close to the total) needs different medicine than thousands of tiny ones (many recalculations, each tiny).
Style recalculation is not holding up your paint. 45 ms of restyling before the page painted, 1.8 % of the time to First Contentful Paint. Nothing here needs attention.
The recalculation work before first paint is 1.8 % of the time to First Contentful Paint.
Blocking requests delay both paints: the browser renders nothing until they arrive, so they push First Contentful Paint and everything after it, including the largest paint (LCP). Requests that block the parser inside the body stall everything after them in the document. Load JavaScript with defer or async, and keep non-critical CSS off the critical path with media attributes. Bars show when each request loaded on a clock that runs to the last paint; the gap after the bars is style and layout work.
| Request | When it loaded | Transfer | Download |
|---|---|---|---|
document | 2.182 s | 55.8 KB | 908 ms |
282 ms | 30.4 KB | 282 ms | |
user.stylesblocking | 114 ms | 1.1 KB | 114 ms |
site.stylesblocking | 114 ms | 3.0 KB | 114 ms |
ext.gadget.SubtleUpdatemarkerblocking | 106 ms | 1.0 KB | 106 ms |
startuppotentially blocking | 157 ms | 22.1 KB | 157 ms |
0630 ms1.260 sFCP · LCP 2.520 s |
Why the browser had to recalculate style and layout: every DOM/style change invalidates some set of nodes, and the same class or attribute churning over and over is the pattern to hunt. Counts, not milliseconds: the time is in the style recalculation numbers above.
Chase what keeps changing after the page is up. 342 style recalculations and 408 layout invalidations fired after first paint, on a page the user was already looking at. The biggest driver is attribute title (28×). Start with the script under "Scripts causing invalidations" that keeps triggering it.
attribute: title28×attribute: class10×attribute: href6×pseudo: link6×pseudo: visited6×pseudo: disabled2×pseudo: enabled2×attribute: disabled1×class: vector-animations-ready1×class: ve-init-mw-desktopArticleTarget-targetContainer1×Invalidations on a page the user was already looking at, the actionable half.
| Reason | Style recalculations | Layout |
|---|---|---|
| A stylesheet rule changed | 152 | – |
| An animation updated stylesAnimate transform and opacity so the compositor can run it off the main thread. | 81 | – |
| A node was inserted into the page | 52 | – |
| Related style rule | 53 | – |
| An @keyframes rule changed | 4 | – |
| An element entered layout | – | 308 |
| A style change forced layout | – | 79 |
| An element's size changed | – | 8 |
| Unknown | – | 8 |
| An SVG element changed | – | 4 |
| Scrollbar changed | – | 1 |
The page being constructed and styled for the first render. Expected work, shown for scale.
| Reason | Style recalculations | Layout |
|---|---|---|
| A stylesheet rule changed | 1 | – |
| A node was inserted into the page | 24 | – |
| An element entered layout | – | 2 212 |
| A style change forced layout | – | 1 |
| An element's size changed | – | 7 |
| Unknown | – | 7 |
| An SVG element changed | – | 3 |
| Scrollbar changed | – | 3 |
3 animations run on the main thread instead of on the browser's fast path that animates without blocking other page work (the compositor); they can make the rendering you see above janky. See them on the CPU tab.
The coach helps you find performance problems on your web page using web performance best practice rules. And gives you advice on privacy and best practices. Tested using Coach-core version 9.2.1.
modernImageFormatsThe page ships 17 images (out of 17) in JPEG/PNG/GIF without a modern alternative. Wrap them in a <picture> with a <source type="image/avif"> or "image/webp" before the legacy <img>, or serve modern formats from your image pipeline directly. AVIF and WebP usually deliver 25–50% smaller files at the same quality.
AVIF and WebP routinely deliver 25–50% smaller files than JPEG and PNG at the same perceived quality, and every browser version still under support understands at least one of them. Ship modern formats either through a <picture> element with <source type="image/avif"> / "image/webp" entries in front of the legacy <img>, or directly from a content-negotiating image pipeline that returns AVIF / WebP when the client accepts it. https://web.dev/articles/serve-images-webp
assetsRedirectsThe page has 67 redirects. 2 of the redirects are from the base domain, please fix them! 65 requests are from other domains, it could be 3rd-party assets doing unnecessary redirects. :(
A redirect is one extra step for the user to download the asset. Avoid that if you want to be fast. Redirects are even more of a showstopper on mobile.
cacheHeadersThe page has 99 requests that are missing a cache time. Configure a cache time so the browser doesn't need to download them every time. It will save 313.3 kB the next access.
The easiest way to make your page fast is to avoid doing requests to the server. Setting a cache header on your server response will tell the browser that it doesn't need to download the asset again during the configured cache time! Always try to set a cache time if the content doesn't change for every request.
documentRedirectThe main document gets redirected 3 time(s). Remove those redirect and make the page faster!
You should never ever redirect the main document, because it will make the page load slower for the user. Well, you should redirect the user if the user tries to use HTTP and there's an HTTPS version of the page. The coach checks for that. :)
javascriptSizeThe total JavaScript transfer size is 291.3 kB and the uncompressed size is 1.2 MB. This is totally crazy! There is really room for improvement here.
A lot of JavaScript often means you are downloading more than you need. How complex is the page and what can the user do on the page? Do you use multiple JavaScript frameworks?
privateAssetsThe page has 58 requests with private headers. The main page has a private header. It could be right in some cases where the user can be logged in and served specific content. But if your asset is static it should never be private. Make sure that the assets really should be private and only used by one user. Otherwise, make it cacheable for everyone.
If you set private headers on content, that means that the content are specific for that user. Static content should be able to be cached and used by everyone. Avoid setting the cache header to private.
lazyLoadingImagesThe page has 16 below-the-fold images without loading="lazy". Add loading="lazy" so the browser defers downloading and decoding them until the user scrolls them into view.
Adding loading="lazy" to an <img> tells the browser not to download or decode it until it is close to the viewport. For images that the user may never see (deep in the page, behind a tab, in a footer carousel), this saves bandwidth and main-thread time during initial render. The LCP image and any image in the initial viewport should NOT be lazy-loaded — that delays the first paint. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#loading
decodingAsyncThe page has 21 images (out of 38) without a decoding hint. Add decoding="async" to non-critical images so the browser can decode them off the main thread.
Setting decoding="async" on an <img> tells the browser it can decode the image off the main thread, which keeps the page responsive to user interactions while images are being processed. The default ("auto") leaves the choice to the browser. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#decoding
avoidScalingImagesThe page has 5 images that are scaled more than 100 pixels. It would be better if those images are sent so the browser don't need to scale them.
It's easy to scale images in the browser and make sure they look good in different devices, however that is bad for performance! Scaling images in the browser takes extra CPU time and will hurt performance on mobile. And the user will download extra kilobytes (sometimes megabytes) of data that could be avoided. Don't do that, make sure you create multiple version of the same image server-side and serve the appropriate one.
firstContentfulPaintFirst contentful paint can be improved (2.520 s). It is in the Google Web Vitals needs improvement range, slower than 1.8 seconds.
The First Contentful Paint (FCP) metric measures the time from when the page starts loading to when any part of the page content is rendered on the screen. For this metric, "content" refers to text, images (including background images), <svg> elements, or non-white <canvas> elements.
cacheHeadersLongThe page has 30 requests that have a shorter cache time than one year (but still a cache time).
Setting a cache header is good. Setting a long cache header (a year) is even better because the asset will stay in the browser cache across visits. For content-hashed URLs (e.g. app.4af2.css) you can safely use Cache-Control: max-age=31536000, immutable. For unversioned URLs that may change, use a revalidating strategy instead.
largestContentfulPaintLargest contentful paint can be improved 2.520 s. It is in the Google Web Vitals needs improvement range, slower than 2.5 seconds.
Largest contentful paint is one of Google Web Vitals and reports the render time of the largest image or text block visible within the viewport, relative to when the page first started loading. To be fast according to Google, it needs to render before 2.5 seconds and results over 4 seconds is poor performance.
longTasksThe page has 1 CPU long task with the total of 96 ms. The total blocking time is 0 ms and 1 long task before first contentful paint with total time of 96 ms. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. Use Geckoprofiler for Firefox or Chromes tracelog to debug your long tasks.
Long CPU tasks locks the thread. To the user this is commonly visible as a "locked up" page where the browser is unable to respond to user input; this is a major source of bad user experience on the web today. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. To debug you should use the Chrome timeline log and drag/drop it into devtools or use Firefox Geckoprofiler.
compressAssetsThe page has 1 request that are served uncompressed. You could save a lot of bytes by sending them compressed instead.
In the early days of the Internet there were browsers that didn't support compressing (gzipping) text content. They do now. Make sure you compress HTML, JSON, JavaScript, CSS and SVG. It will save bytes for the user; making the page load faster and use less bandwith.
| URL | Transfer | Content |
|---|---|---|
| https://en.wikipedia.org/wiki/Main_Page | 55.8 KB | 253.0 KB |
optimalCssSizehttps://en.wikipedia.org/w/load.php?lang=en&modules=ext.echo.styles.alert%2Cbadge%7Cext.personalDashboard.menuIcon%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediamessages.styles%7Cmediawiki.codex.messagebox.styles%7Cmediawiki.skinning.content.parsoid%7Cmediawiki.skins.legacy%7Coojs-ui.styles.icons-alerts%7Cskins.vector.icons%2Cstyles%7Cskins.vector.search.codex.styles%7Cwikibase.client.init&only=styles&skin=vector-2022 size is 31.2 kB (31176) and that is bigger than the limit of 25 kB. Try to keep each CSS response under 25 kB.
Render-blocking CSS holds up the first paint until it has fully downloaded, parsed and applied, so smaller CSS files mean a faster start. Split your CSS into a small critical bundle inlined or eagerly loaded, with the rest lazy-loaded.
| URL | Transfer | Content |
|---|---|---|
| https://en.wikipedia.org/w/load.php...ia.org/w/load.php | 30.4 KB | 266.9 KB |
inlineCssThe page has both inline CSS and CSS requests even though it uses a HTTP/2-ish connection. If you have many users on slow connections, it can be better to only inline the CSS. Run your own tests and check the waterfall graph to see what happens.
In the early days of the Internet, inlining CSS was one of the ugliest things you can do. That has changed if you want your page to start rendering fast for your user. Always inline the critical CSS when you use HTTP/1 and HTTP/2 (avoid doing CSS requests that block rendering) and lazy load and cache the rest of the CSS. It is a little more complicated when using HTTP/2. Does your server support HTTP push? Then maybe that can help. Do you have a lot of users on a slow connection and are serving large chunks of HTML? Then it could be better to use the inline technique, becasue some servers always prioritize HTML content over CSS so the user needs to download the HTML first, before the CSS is downloaded.
metaDescriptionThe page is missing a meta description.
Use a page description to make the page more relevant to search engines.
unnecessaryHeadersThere are 86 responses that sets both a max-age and expires header. There are 136 responses that sets a server header.
Do not send headers that you don't need. We look for p3p, cache-control and max-age, pragma, server and x-frame-options headers. Have a look at Andrew Betts - Headers for Hackers talk as a guide https://www.youtube.com/watch?v=k92ZbrY815c or read https://www.fastly.com/blog/headers-we-dont-want.
viewportThe viewport meta tag does not contain width=device-width, the browser may use a desktop-width fallback.
The viewport meta tag tells the browser how to lay out the page on small screens. Without it (or without width=device-width) the page is rendered at a desktop fallback width and scaled down, which makes text unreadable on mobile. Disabling zoom (user-scalable=no, maximum-scale<=1) is also an accessibility regression. https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag
longHeadershttps://en.wikipedia.org/wiki/Main_Page has a header set-cookie that is 1950 characters long. https://en.wikipedia...ia.org/w/load.php has a header sourcemap that is 1244 characters long.
Do not send response headers that are too long.
contentSecurityPolicyHeaderSet a Content-Security-Policy header to mitigate cross-site scripting attacks. You can start with a Content-Security-Policy-Report-Only header, which only reports violations rather than blocking them.
A Content-Security-Policy response header tells the browser which sources of script, style, and other content are allowed. The most effective form is a strict CSP using nonces or hashes together with strict-dynamic; the worst is a missing header, with unsafe-inline and unsafe-eval close behind. https://web.dev/articles/strict-csp
crossOriginEmbedderPolicyHeaderSet a Cross-Origin-Embedder-Policy header (typically require-corp or credentialless) on the document response to control cross-origin embedding.
Cross-Origin-Embedder-Policy (COEP) makes the page refuse to load cross-origin subresources unless they explicitly opt in via CORP or CORS. Together with Cross-Origin-Opener-Policy it puts the page in a cross-origin isolated context, which mitigates cross-window side-channel attacks (Spectre) and unlocks high-resolution timers and SharedArrayBuffer. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Embedder-Policy
crossOriginOpenerPolicyHeaderSet a Cross-Origin-Opener-Policy header (typically same-origin) on the document response to isolate the page from cross-origin windows.
Cross-Origin-Opener-Policy (COOP) lets a page sever its window-group ties to cross-origin documents that opened it or that it opens. Together with Cross-Origin-Embedder-Policy it puts the page in a cross-origin isolated context, which mitigates cross-window side-channel attacks (Spectre) and unlocks high-resolution timers and SharedArrayBuffer. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy
crossOriginResourcePolicyHeaderSet a Cross-Origin-Resource-Policy header (same-origin, same-site or cross-origin) on the document response to limit who may embed it.
Cross-Origin-Resource-Policy (CORP) is a per-response opt-in that tells the browser which origins are allowed to embed the resource. It blocks cross-origin or cross-site no-cors embedding (img, script, iframe, etc.) and is one of the building blocks of cross-origin isolation. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Resource-Policy
permissionsPolicyHeaderSet a Permissions-Policy header to control which browser features the page can use.
The Permissions-Policy response header (the successor to Feature-Policy) lets a site explicitly opt in or out of powerful browser features such as camera, microphone, geolocation, payment and clipboard. Setting a strict policy reduces the attack surface and limits what embedded third parties can do. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Permissions-Policy
referrerPolicyHeaderSet a referrer-policy header to make sure you do not leak user information.
Referrer Policy is a new header that allows a site to control how much information the browser includes with navigations away from a document and should be set by all sites. https://scotthelme.co.uk/a-new-security-header-referrer-policy/.
A snapshot of what the browser actually built for this page: the document, how big and deep the DOM tree is and what it kept in storage. Big, deep trees are slower to style and lay out, so the counts Chrome warns about carry a flag.
Document
What the page says it is and how large it rendered.
DOM structure
How much markup the browser has to build, style and lay out.
What the page stored on the client, and the network it was tested on.
Data collected using
Coach-core version 9.2.1. With updated code from
Webappanalyzer 2026-05-04. Use
--browsertime.firefox.includeResponseBodies html or
--browsertime.chrome.includeResponseBodies html to help Wappalyzer find more information about technologies used.
0.0s2.3s2.5s2.6s2.8s2.9s3.1s3.3sWhen the page main content is rendered, collected via the Largest Contentful Paint API. Read more about Largest Contentful Paint.
body > div:eq(2) > div > div:eq(2) > main#content > div#bodyContent > div#mw-content-text > div:eq(1) > section#mwAQ > div#mp-upper > div#mp-left > div#mp-tfa > p
The LCP element is highlighted in the screenshot. If nothing is highlighted the element was removed before the screenshot or the LCP API couldn't find it.
How much the page's content shifts as it loads, collected via the Cumulative Layout Shift API.
One shift is 100% of your 0.001 CLS. div#p-wikibase-otherprojects moved at 2.799 s. Reserve space for whatever renders into that spot, a fixed height or an aspect-ratio box, so later content stops pushing the page around.
Worst first, showing shifts of 0.01 and up. Each percentage is that shift's exact share of the score.
The shift is spread across many movements below 0.01, none large enough to single out. Check the video or filmstrip to see what moved.
Elements that shifted by more than 0.01 are highlighted in the screenshot. If an element shifted outside the viewport, it won't appear here. Check the video or filmstrip to see the shift.
Timing data the server chose to expose through Server-Timing response headers on the main document — typically backend time, cache status or experiment flags.
| Name | Duration | Description |
|---|---|---|
WMF-Uniq | 0 ms | we-1-8-account-creation-no-desktop-benefits=treatment; |
co_id | 0 ms | 2872071467 |
There are no custom configured scripts.
There are no custom extra metrics from scripting.
How the page is built.
https://en.wikipedia.org/wiki/Main_Page
| Header | Value |
|---|---|
accept-ch | Sec-CH-UA, Sec-CH-UA-Arch, Sec-CH-UA-Bitness, Sec-CH-UA-Form-Factor, Sec-CH-UA-Full-Version-List, Sec-CH-UA-Mobile, Sec-CH-UA-Model, Sec-CH-UA-Platform, Sec-CH-UA-Platform-Version, Sec-CH-UA-WoW64 |
age | 0 |
cache-control | private, max-age=0, s-maxage=0 |
content-length | 0 |
content-type | text/html; charset=UTF-8 |
date | Tue, 28 Jul 2026 02:43:04 GMT |
expires | Thu, 01 Jan 1970 00:00:00 GMT |
location | https://en.wikipedia.org/w/index.php?title=Special:UserLogin/return&returnto=Main+Page&wpLoginToken=d014808f3a33cc6469fc693f66baa6eb6a681724%2B%5C&useformat=desktop&usesul3=1¢ralauthLoginToken=629cdff66125016c0b62d31f07a4b7aa |
nel | { "report_to": "wm_nel", "max_age": 604800, "failure_fraction": 0.05, "success_fraction": 0.0} |
report-to | { "group": "wm_nel", "max_age": 604800, "endpoints": [{ "url": "https://intake-logging.wikimedia.org/v1/events?stream=w3c.reportingapi.network_error&schema_uri=/w3c/reportingapi/network_error/1.0.0" }] } |
server | mw-web.eqiad.main-5fc9744499-6k26v |
server-timing | cache;desc="pass", host;desc="cp3070",co_id;desc="1201615530" |
strict-transport-security | max-age=106384710; includeSubDomains; preload |
vary | Accept-Encoding,X-Forwarded-Proto,Cookie,Authorization |
x-analytics | |
x-cache | cp3070 miss, cp3070 pass |
x-cache-status | pass |
x-client-ip | 138.201.135.103 |
x-content-type-options | nosniff |
x-request-id | 2b2e5372-a48e-4848-bd05-486f80d66a11 |
Transfer size760.1 KB
Content size2.0 MB
Requests69
| Content | Header Size | Transfer Size | Content Size | Requests |
|---|---|---|---|---|
| html | 0 b | 55.8 KB | 253.0 KB | 1 |
| css | 0 b | 35.6 KB | 274.3 KB | 4 |
| javascript | 0 b | 284.4 KB | 1.1 MB | 8 |
| image | 0 b | 306.0 KB | 234.6 KB | 33 |
| favicon | 0 b | 1.8 KB | 2.7 KB | 1 |
| svg | 0 b | 75.6 KB | 144.7 KB | 21 |
| plain | 0 b | 924 B | 0 b | 1 |
| Total | 0 b | 760.1 KB | 2.0 MB | 69 |
| Domain | Total download time | Transfer Size | Content Size | Requests |
|---|---|---|---|---|
| auth.wikimedia.org | 8.835 s | N/A | 0 b | 33 |
| en.wikipedia.org | 8.506 s | 454.1 KB | 1.8 MB | 38 |
| upload.wikimedia.org | 11.748 s | 264.5 KB | 233.5 KB | 17 |
| en.wikibooks.org | 815 ms | 2.8 KB | 68 B | 3 |
| en.wikinews.org | 921 ms | 2.8 KB | 68 B | 3 |
| en.wikiquote.org | 982 ms | 4.1 KB | 68 B | 3 |
| en.wikisource.org | 935 ms | 2.9 KB | 68 B | 3 |
| en.wikiversity.org | 741 ms | 2.9 KB | 68 B | 3 |
| en.wikivoyage.org | 743 ms | 2.9 KB | 68 B | 3 |
| en.wiktionary.org | 747 ms | 2.9 KB | 68 B | 3 |
| www.mediawiki.org | 996 ms | 2.9 KB | 68 B | 3 |
| commons.wikimedia.org | 755 ms | 2.7 KB | 68 B | 3 |
| foundation.wikimedia.org | 1.077 s | 1.2 KB | 68 B | 3 |
| incubator.wikimedia.org | 780 ms | 2.7 KB | 68 B | 3 |
| meta.wikimedia.org | 641 ms | 2.7 KB | 68 B | 3 |
| species.wikimedia.org | 728 ms | 2.7 KB | 68 B | 3 |
| wikimania.wikimedia.org | 683 ms | 1.2 KB | 68 B | 3 |
| www.wikidata.org | 1.076 s | 2.8 KB | 68 B | 3 |
| www.wikifunctions.org | 1.034 s | 1.4 KB | 68 B | 3 |
| type | min | median | max |
|---|---|---|---|
| Expires | 0 seconds | 0 seconds | 1 year |
| Last modified | 2 minutes | 4 weeks | 2 years |
Includes requests done after load event end.
| Content | Transfer Size | Requests |
|---|---|---|
| html | 0 b | 0 |
| css | 0 b | 0 |
| javascript | 0 b | 0 |
| image | 0 b | 0 |
| font | 0 b | 0 |
| favicon | 1.8 KB | 1 |
| plain | 924 B | 1 |
| Total | 2.7 KB | 2 |
Includes requests done after DOM content loaded.
| Content | Transfer Size | Requests |
|---|---|---|
| html | 0 b | 0 |
| css | 0 b | 0 |
| javascript | 30.8 KB | 3 |
| image | 41.5 KB | 16 |
| font | 0 b | 0 |
| favicon | 1.8 KB | 1 |
| svg | 6.0 KB | 5 |
| plain | 924 B | 1 |
| Total | 81.0 KB | 85 |
Tasks ≥ 50 ms blocking the main thread, collected via the Long Task API.
A long animation frame (LOAF) is a frame that took ≥ 50 ms from input to the next paint. The part beyond the threshold is blocking time, the number that hurts Interaction to Next Paint and Total Blocking Time. Break long tasks up (scheduler.yield(), smaller chunks) or move the work off the main thread. Read more about the Long Animation Frames API.
| Script | Frames | Time running | Blocking (share by run time) | Forced style & layout | Triggered by |
|---|---|---|---|---|---|
| load.php[startup] | 2 | 60.1 ms | 8.3 ms | – | script tag, timer or animation callback |
A frame's blocking time is split between its scripts by their share of the frame's work, capped at each script's own run time — blocking from work no script owns (HTML parsing, browser internals) stays unattributed. The per-script blocking view below uses the same attribution.
How much each script blocked the main thread, derived from the Long Animation Frame API. Each frame's blocking time is split between its scripts by their share of the frame's work, capped at each script's own run time — blocking from work no script owns (HTML parsing, browser internals) is not attributed (older data credits the script that started the frame). The closest answer to "which script should I fix to improve TBT" the platform exposes.
Total Blocking Time attributed per script from the Chrome trace: every main-thread task longer than 50 ms blocks input for the remainder, and each blocking task is credited to the script whose own code ran the longest during that task.
All main-thread work during the full page load, not just the share that blocked input. Calculated from the Chrome trace.
parseHTMLstyleLayoutscriptParseCompilescriptEvaluationpaintCompositeRendergarbageCollectionotherThe functions where main-thread JavaScript time was actually spent, sampled by Chrome's JavaScript profiler. Self time is spent in the function itself; total time includes the functions it called. For loader/dispatcher functions whose total dwarfs their self time, the runs line shows the top functions and modules (up to five, ≥ 1 ms) the total was actually spent running.
| Function | Where | Self time | Total time |
|---|---|---|---|
flushWritesruns: load.php[startup] (3.7 ms) | load.php[startup] | 17.6 ms | 21.4 ms |
setTimeout | 8.9 ms | 8.9 ms | |
runScriptruns: load.php[scripts:ext.centralNotice.bannerHistoryLogger] (29.7 ms), load.php[scripts:ext.cite.referencePreviews] (4.7 ms) | load.php[startup] | 7.6 ms | 70.3 ms |
insertBefore | 7.2 ms | 7.2 ms | |
require | load.php[startup] | 6.1 ms | 12.7 ms |
updateTooltipOnElement | load.php[scripts:ext.centralNotice.bannerHistoryLogger] | 4.2 ms | 4.5 ms |
appendChild | 3.9 ms | 4.4 ms | |
impl | load.php[startup] | 3.5 ms | 5.0 ms |
doPropagationruns: load.php[startup] (40.7 ms), load.php[scripts:ext.centralNotice.bannerHistoryLogger] (1.7 ms) | load.php[startup] | 3.3 ms | 46.8 ms |
set | load.php[startup] | 3.0 ms | 3.7 ms |
querySelectorAll | 2.9 ms | 2.9 ms | |
requestIdleCallback | 2.8 ms | 2.8 ms | |
(anonymous) | load.php[scripts:ext.centralNotice.bannerHistoryLogger] | 2.2 ms | 2.4 ms |
findruns: querySelectorAll (2.0 ms), load.php[scripts:ext.centralNotice.bannerHistoryLogger] (1.9 ms) | load.php[scripts:ext.centralNotice.bannerHistoryLogger] | 2.1 ms | 6.7 ms |
eachruns: load.php[scripts:ext.centralNotice.bannerHistoryLogger] (11.2 ms) | load.php[scripts:ext.centralNotice.bannerHistoryLogger] | 2.0 ms | 17.6 ms |
How much setTimeout/setInterval work the page runs, credited to the script that scheduled each timer. Many zero-delay timers mean work sliced into a machine-gun of tiny tasks; repeating timers are polling.
| Set by | Delay | Type | Times set | Times fired | Fire time |
|---|---|---|---|---|---|
| load.php[scripts:ext.centralNotice.bannerHistoryLogger]:433 | 0 ms | once | 47 | 47 | 31.2 ms |
| load.php[scripts:ext.centralNotice.bannerHistoryLogger]:435 | 0 ms | once | 1 | 1 | 1.5 ms |
SafeStorage in load.php[scripts:ext.centralNotice.bannerHistoryLogger]:688 | 2000 ms | once | 2 | 2 | 0.9 ms |
sendEvent in load.php[scripts:ext.centralNotice.bannerHistoryLogger]:164 | 5000 ms | once | 1 | 1 | 0.7 ms |
| load.php[scripts:ext.centralNotice.bannerHistoryLogger]:150 | 0 ms | once | 1 | 1 | 0.4 ms |
requestUpdate in load.php[startup]:22 | 2000 ms | once | 1 | 1 | 0.1 ms |
| load.php[scripts:ext.centralNotice.bannerHistoryLogger]:106 | 60000 ms | once | 1 | 0 | 0.0 ms |
run in load.php[scripts:ext.centralNotice.bannerHistoryLogger]:209 | 60000 ms | once | 1 | 0 | 0.0 ms |
setActive in load.php[scripts:ext.centralNotice.bannerHistoryLogger]:209 | 100000 ms | once | 1 | 0 | 0.0 ms |
Main-thread CPU time from the Chrome trace split by domain. First party is wikipedia.org.
Animations that fell back from the compositor to the main thread, blocking each frame instead of running on the GPU.
Each chip below is a CSS property the page tried to animate that Chrome couldn't hand to the compositor. Swap it for a transform or opacity equivalent where you can.
max-height1×top1×Want to dig deeper? Download the Chrome trace and drag-and-drop it into Performance in DevTools.