Tested 2026-08-17 06:54:32 using Chrome 151.0.7922.75 (runtime settings)
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.
Rendering was not meaningfully delayed. First paint landed at 548 ms on a 117 ms first byte; the 16 render-blocking requests were done by 240 ms and the remaining ~308 ms is style, layout and web-font loading.
Want to see how much CSS style-recalculation work delayed FCP and LCP, plus CPU long tasks? Run with --cpu.
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. Web fonts are context, not blockers: text renders invisible or in a fallback face while they load, so a font finishing after a paint is the classic reason text changed late.
| Request | When it loaded | Transfer | Download |
|---|---|---|---|
document | 51 ms | 85 B | 50 ms |
85 ms | 69.5 KB | 85 ms | |
84 ms | 34.1 KB | 84 ms | |
83 ms | 16.4 KB | 83 ms | |
primer-73a0e2225731ad3f.cssblocking | 82 ms | 42.3 KB | 82 ms |
global-558303a14f5c5e97.cssblocking | 81 ms | 39.9 KB | 81 ms |
home-31205358851b685e.cssblocking | 80 ms | 7.0 KB | 80 ms |
github-59fc16002818df36.cssblocking | 80 ms | 21.4 KB | 80 ms |
64 ms | 3.6 KB | 64 ms | |
| 12 more requests | all done by 235 ms | 42.4 KB | |
143 ms | 214.6 KB | 143 ms | |
0137 ms274 msFCP · LCP 548 ms |
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.
longTasksThe page has 6 CPU long tasks with the total of 472 ms. The total blocking time is 52 ms and 2 long tasks before first contentful paint with total time of 220 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.
cssSizeThe total CSS transfer size is 291.9 kB and uncompressed size is 2.4 MB. I don't know what to say, the page needs more than 2 MB CSS to render.
Delivering a massive amount of CSS to the browser is not the best thing you can do, because it means more work for the browser when parsing the CSS against the HTML and that makes the rendering slower. Try to send only the CSS that is used on that page. And make sure to remove CSS rules when they aren't used anymore.
documentRedirectThe main document gets redirected 1 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 1.7 MB and the uncompressed size is 7.4 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?
pageSizeThe page total transfer size is 3.8 MB, which is more than the coach limit of 3 MB. That is really big and you need to make it smaller.
Avoid having pages that have a transfer size over the wire of more than 3 MB (desktop) and 2 MB (mobile) because heavy pages hurt performance and are expensive for users on metered connections. Reference: HTTP Archive median page weight in 2024 was around 2.7 MB desktop / 2.4 MB mobile, so this rule fires when a page is above the modern median.
decodingAsyncThe page has 21 images (out of 24) 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
optimalCssSizehttps://github.githubassets.com/assets/primer-73a0e2225731ad3f.css size is 43.3 kB (43328) and that is bigger than the limit of 25 kB. https://github.githubassets.com/assets/global-558303a14f5c5e97.css size is 40.9 kB (40862) and that is bigger than the limit of 25 kB. https://github.githubassets.com/assets/primer-react-css.5f9c19d1f6c8e3e3.module.css size is 34.9 kB (34889) and that is bigger than the limit of 25 kB. https://github.githubassets.com/assets/primer-react-brand-css.566b06f97d781cc2.module.css size is 71.2 kB (71219) 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://github.githubassets.com/assets/primer-73a0e2225731ad3f.css | 42.3 KB | 402.3 KB |
| https://github.githubassets.com/assets/global-558303a14f5c5e97.css | 39.9 KB | 290.7 KB |
| https://github.githubassets.com/assets/primer-react-css.5f9c19d1f6c8e3e3.module.css | 34.1 KB | 284.8 KB |
| https://github.githubassets.com/assets/primer-react-brand-css.566b06f97d781cc2.module.css | 69.5 KB | 678.0 KB |
cacheHeadersThe page has 3 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 2.7 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.
fewFontsThe page has 2 font requests. Do you really need them? What value does the fonts give the user?
How many fonts do you need on a page for the user to get the message? Fonts can slow down the rendering of content, try to avoid loading too many of them because worst case it can make the text invisible until they are loaded (FOIT—flash of invisible text), best case they will flicker the text content when they arrive.
modernImageFormatsThe page ships 3 images (out of 19) 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
spofThe page has 22 requests inside of the head that can cause a SPOF (single point of failure). Load them asynchronously or move them outside of the document head.
A page can be stopped from loading in the browser if a single JavaScript, CSS, and in some cases a font, couldn't be fetched or is loading really slowly (the white screen of death). That is a scenario you really want to avoid. Never load 3rd-party components synchronously inside of the head tag.
assetsRedirectsThe page has 1 redirect. 1 request 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.
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://github.com/ | 119.7 KB | 561.0 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.
mimeTypesThe page has 5 misconfigured mime types.
It's not a great idea to let browsers guess content types (content sniffing), in some cases it can actually be a security risk.
cacheHeadersLongThe page has 1 request 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.
unnecessaryHeadersThere are 146 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.
metaDescriptionThe meta description is too long. It has 186 characters, the recommended max is 160
Use a page description to make the page more relevant to search engines.
pageTitleThe title is too long by 1 characters. The recommended max is 60
Use a title to make the page more relevant to search engines.
longHeadershttps://github.com/manifest.json has a header content-security-policy that is 3600 characters long.
Do not send response headers that are too long.
referrerPolicyNo <meta name="referrer"> tag was found on the page. Set a Referrer-Policy response header (preferred) or add a meta tag, for example <meta name="referrer" content="strict-origin-when-cross-origin">.
Without an explicit referrer policy the browser falls back to the user-agent default and may leak the full URL of the previous page (including query strings) to every cross-origin request. Set a Referrer-Policy response header (preferred) or a <meta name="referrer"> tag in the document. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy
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
nelHeaderSet a NEL header (paired with Reporting-Endpoints) to collect connection-level error reports from the field.
The NEL (Network Error Logging) response header tells the browser to record connection-level failures (DNS, TLS, HTTP errors) and ship them to a reporting endpoint. NEL pairs with the Reporting-Endpoints / Report-To header — the page declares the endpoint group and NEL points at it. Together they give you visibility into errors that never reach your origin server. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/NEL
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/.
reportingEndpointsHeaderSet a Reporting-Endpoints header (or the legacy Report-To header) so CSP reports, NEL data and other Reporting-API events have an endpoint to land at.
The Reporting-Endpoints response header (the successor to Report-To) names the URLs that browsers should POST reports to. Without it, CSP report-to directives, Cross-Origin-Opener-Policy reports, NEL data and other Reporting-API events have nowhere to go. The legacy Report-To header is still accepted for older Chromium versions. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Reporting-Endpoints
xContentTypeOptionsHeaderSet X-Content-Type-Options: nosniff on the document response to prevent MIME-sniffing.
X-Content-Type-Options: nosniff prevents browsers from interpreting files as a different MIME type than what is declared in the Content-Type header. This blocks a class of cross-site scripting and content-type confusion attacks and should be set on every response. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
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.
0.0s0.3s0.5s0.6s0.8s0.9s1.1s1.2sWhen the page main content is rendered, collected via the Largest Contentful Paint API. Read more about Largest Contentful Paint.
body > div:eq(0) > div:eq(7) > main > react-app > div > div > div > section#hero > div:eq(0) > div:eq(4) > section > div > div > div > h1#hero-section-brand-heading
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 0.047 CLS. div:eq(0) moved at 946 ms. 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.
body > div:eq(0) > div:eq(7) > main > react-app > div > div > div > section#hero > div:eq(0) > div:eq(0)
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.
There are no custom configured scripts.
There are no custom extra metrics from scripting.
How the page is built.
| Header | Value |
|---|---|
content-length | 0 |
location | https://github.com/ |
strict-transport-security | max-age=31536000; includeSubDomains; preload |
Transfer size3.6 MB
Content size11.8 MB
Requests147
| Content | Header Size | Transfer Size | Content Size | Requests |
|---|---|---|---|---|
| html | 0 b | 119.7 KB | 561.0 KB | 1 |
| css | 0 b | 285.1 KB | 2.3 MB | 25 |
| javascript | 0 b | 1.7 MB | 7.0 MB | 96 |
| image | 0 b | 551.0 KB | 546.1 KB | 13 |
| font | 0 b | 251.5 KB | 250.7 KB | 2 |
| other | 0 b | 811.6 KB | 806.8 KB | 5 |
| plain | 0 b | 989 B | 0 b | 3 |
| svg | 0 b | 1.3 KB | 959 B | 1 |
| video | 0 b | 0 b | 384.0 KB | 1 |
| Total | 0 b | 3.6 MB | 11.8 MB | 147 |
| Domain | Total download time | Transfer Size | Content Size | Requests |
|---|---|---|---|---|
| www.github.com | 69 ms | N/A | 0 b | 1 |
| github.com | 185 ms | 124.3 KB | 562.5 KB | 2 |
| github.githubassets.com | 14.479 s | 3.5 MB | 11.3 MB | 142 |
| collector.github.com | 557 ms | 989 B | 0 b | 2 |
| api.github.com | 137 ms | 0 b | 0 b | 1 |
| type | min | median | max |
|---|---|---|---|
| Expires | 0 seconds | 1 year | 1 year |
| Last modified | 2 days | 2 weeks | 2 years |
Includes requests done after load event end.
| Content | Transfer Size | Requests |
|---|---|---|
| html | 0 b | 0 |
| css | 907 B | 1 |
| javascript | 30.0 KB | 4 |
| image | 551.0 KB | 13 |
| font | 0 b | 0 |
| favicon | 0 b | 0 |
| plain | 989 B | 3 |
| svg | 1.3 KB | 1 |
| other | 807.0 KB | 4 |
| video | 0 b | 1 |
| Total | 1.4 MB | 27 |
Includes requests done after DOM content loaded.
| Content | Transfer Size | Requests |
|---|---|---|
| html | 0 b | 0 |
| css | 907 B | 1 |
| javascript | 30.0 KB | 4 |
| image | 551.0 KB | 13 |
| font | 0 b | 0 |
| favicon | 0 b | 0 |
| plain | 989 B | 3 |
| svg | 1.3 KB | 1 |
| other | 807.0 KB | 4 |
| video | 0 b | 1 |
| Total | 1.4 MB | 27 |
Third party requests categorised by Third party web version 0.29.2.
No third-party requests detected
Every request on this page resolved to a first-party domain. There are no entries in Third party web to attribute, no third-party tools to enumerate, and no third-party cookies set. If you expected to see entries here you can fine-tune the first-party domain list with --firstParty.
Calculated using .*github.* (use --firstParty to configure).
| Content | Header Size | Transfer Size | Content Size | Requests |
|---|---|---|---|---|
| html | 0 b | 119.7 KB | 561.0 KB | 1 |
| css | 0 b | 285.1 KB | 2.3 MB | 25 |
| javascript | 0 b | 1.7 MB | 7.0 MB | 96 |
| image | 0 b | 551.0 KB | 546.1 KB | 13 |
| font | 0 b | 251.5 KB | 250.7 KB | 2 |
| favicon | 0 b | 0 b | 0 b | 0 |
| other | 0 b | 811.6 KB | 806.8 KB | 5 |
| plain | 0 b | 989 B | 0 b | 3 |
| svg | 0 b | 1.3 KB | 959 B | 1 |
| video | 0 b | 0 b | 384.0 KB | 1 |
| Total | N/A | 3.6 MB | 11.8 MB | 148 |