Font-Display Optional Vs Swap

31 May 2022

Font-Display Options – Optional Vs Swap:

When using CSS, you have the option of displaying one or both fonts. This option has two advantages: fallback fonts and a short waiting period. This wait time can be 100ms or 3s. With Fallback, a font is displayed in case it is unavailable. So, read the article to get information on this Font-Display Optional Vs Swap.

However, this option will prevent a late-term swap or FOUT. If you want to use both fallback and swap, make sure you use the same style.

Fallback font:

Font display options: Swap and Optional give the user different levels of control when it comes to choosing what is displayed on a page. Optional displays fallback fonts after 100ms of inactivity, while swap displays fallbacks after an infinite time period.

For best results, use Swap when you have an important font. This setting will help you render text correctly in any font without worrying about latency. The font-display descriptor determines which font face to display. By default, auto uses the user agent’s font display strategy.

The fallback strategy, however, is similar to block. When the user agent doesn’t find a suitable font, it uses its own default strategy. However, if it’s not available, it uses an anonymous font face. This font face contains the glyphs without any “ink.” It’s best to use this mode when rendering text in a particular typeface.

Block period:

If you’re wondering how to use block period to change font display, the answer is simple. The block period is the time frame when a browser waits for the font to be available before rendering the text. It’s generally less than three seconds and should help prevent late layout shifts.

The swapping font is used when the desired font is not available, or when the browser doesn’t have time to download it. Optional vs Swap is best for testing your website. The latter will be useful for testing and debugging purposes.

The former will let you change the font display while the latter will force the browser to display the default font. While swapping fonts can lead to page shifting, block period font display prevents it. It’s recommended that you use a block period to prevent unexpected layout shifts.

Swap period:

The two most common differences between optional font display and swap period are their block period and swap period. Blocks have a zero-second block period, while swap has an infinite swap period. Typically, swap is used when the specific font is important for the page, but rendering in a fallback is acceptable as long as the user can still read the text.

A good example of an application that would benefit from swap is logo text, which can be rendered using a reasonable fallback font. Similarly, company names can be displayed using an official typeface. While font-display is the default setting for CSS, swaps can have different behavior.

When an external font is not available, the website will load a fallback font based on its size and style. If the font doesn’t load within the swap period, it will display fallback text instead. If swapping the font is not possible, the page will not display text until the external font is loaded.

Invisibility period:

When used together, font-display options allow you to specify a minimum block period for the face of the font. An optional value guarantees that a browser does not swap fonts until the block period is reached. Using swap instead of optional means the browser will use a fallback font if the font face is not loaded.

However, the fallback font is displayed only for a brief period of time and then the user will be able to read the content of the page. When using an optional font-display property, you’ll want to use a font with an invisibility period of three seconds.

This way, your text will appear without the fallback font for a short amount of time. In contrast, the default font is loaded after a block period, so when it does load, it’ll be displayed. If, however, you want a custom font, you can use the swap-period option.

Layout shifts:

Layout shifts caused by unexpected font-display values can cause minor operating problems. Font-display values can be modified in CSS to change the font rendering behavior in HTML. Layout shifts that occur within 500 ms of user input are not considered CLS.

This issue may be resolved by reserving minimum space for fonts. Font-display values can affect the loading time of a page. Users should avoid unexpected layout shifts in HTML. Especially if the shift occurs without the user’s knowledge, users may become frustrated.


To detect layout shifts and improve the user experience, you can use the Cumulative Layout Shift metric. This metric is part of Google’s ranking algorithm. Ideally, you should strive to minimize your site’s CLS. By optimizing your site’s layout, you can improve UX and SEO.


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