Critical Path CSS Generator
Penthouse is the original critical path css generator, helping you out to speed up page rendering for your websites. Supply your site's full CSS and the page you want to create the critical CSS for, and Penthouse will return the critical CSS needed to perfectly render the above the fold content of the page. Read more about critical path css here.
The process is automatic and the generated CSS is production ready as is. Behind the scenes Penthouse is using puppeteer to generate the critical css via the chromium:headless.
(If you don’t want to write code, you can use the online hosted version.)
yarn add --dev penthouse
npm install, if not using yarn)
Performance when running many jobs
Penthouse is optimised for running many jobs in parallel. One shared browser instance is re-used and each job runs in its own browser tab. There's only so many jobs you can run in parallel before your machine starts running out of resources. To run many jobs effectively, see the many urls example.
cssString are required - all other options are optional. Note that the html file found via
url is expected to be styled;
penthouse does not inject any styles, it just uses
css) to prune into critical css.
||Accessible url. Use
||Original css to extract critical css from|
||Path to original css file on disk (if using instead of
||Width for critical viewport|
||Height for critical viewport|
||Configuration for screenshots (not used by default). See Screenshot example|
||Keep media queries even for width/height values larger than critical viewport.|
||Array of css selectors to keep in critical css, even if not appearing in critical viewport. Strings or regex (f.e.
||Css properties to filter out from critical css|
||Ms; abort critical CSS generation after this time|
||Settings for puppeteer. See Custom puppeteer browser example|
||Ms; stop waiting for page load after this time (for sites when page load event is unreliable)|
||ms; wait time after page load before critical css extraction starts (also before "before" screenshot is taken, if used)|
||set to false to load JS (not recommended)|
||characters; strip out inline base64 encoded resources larger than this|
||Can be specified to limit nr of elements to inspect per css selector, reducing execution time.|
||specify which user agent string when loading the page|
||Set extra http headers to be sent with the request for the url.|
||For formatting of each cookie, see Puppeteer setCookie docs|
||Make Penthouse throw on errors parsing the original CSS. Legacy option, not recommended.|
Enable debug logging
# Basic verbose logging for all componentsenv DEBUG="penthouse,penthouse:*" node script.js
Not working on Linux
Install missing dependencies to get the headless Chrome to run:
sudo apt-get install libnss3
You might possibly need an even longer list of deps, depending on your dist, see this answer
Problems with generated CSS
A good first step can be to test your url + css in the hosted critical path css generator, to determine whether the problem is with the input your passing (css + url), or with your local setup: https://jonassebastianohlsson.com/criticalpathcssgenerator
Unstyled content showing when using the critical css
If you see flashes of unstyled content showing after applying your critical css then something is wrong. Below are the most commont causes and some general related advice:
Your page contains dynamic or JS injected/activated content.
If your html is fine, but varies based on things such as the logged in user, third party advertising etc, then you can use the
forceInclude parameter to force specific extra styles to remain in the critical css, even if Penthouse doesn’t see them on the page during critical css generation.
Early DOM content moved out of critical viewport via CSS
This problem can happen if you have an element appearing early in the DOM, but with styles applied to move outside of the critical viewport (using absolute position or transforms). Penthouse does not look at the absolute position and transform values and will just see the element as not being part of the critical viewport, and hence Penthouse will not consider it’s styles critical (so the unstyled element will show when the critical css is used).
Solution: Consider whether it really should appear so early in the DOM, or use the
forceInclude property to make sure the styles to "hide"/move it are left in the critical css.
Special glyphs not showing/showing incorrectly
Problems with special characters like → after converting? Make sure you use the correct hexadecimal format in your CSS. You can always get this format from your browser console, by entering '→'
.charCodeAt(0).toString(16) (answer for this arrow glyph is
2192). When using hexadecimal format in CSS it needs to be prepended with a backslash, like so: