Best practice: optimizing fonts

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In recent years, the use of fonts on the web has exploded (both in terms of the number of existing fonts and the number of sites using them).

As usual, the Web Almanac is a mine of information, especially via the chapter dedicated to fonts. We learn that the two main suppliers of web fonts are Google and Font Awesome, the latter consisting in the provision of icons. Beyond the potential cost on performance and environmental impacts, some countries have already established that this could contravene the GDPR (General Data Protection Regulation).

Proportion of websites using web fonts

Let’s see what good practices can reduce the impact of fonts on the web.

Existing reference systems

The fonts are mentioned in the UX/UI family of the RGESN (Référentiel Général d’écoconception de services numériques) :

  • 4.10 – Does the digital service use mostly operating system fonts?

They are also found in GR491 (Responsible Digital Service Design Reference Guide):

Finally, the 115 web ecodesign best practices also mention them:

Good practices


In order to reduce the impacts of fonts, several best practices are applicable:

  • Give preference to standard/ system fonts : This avoids additional requests
  • Use an optimal compression format (today, it is the WOFF2 format). Online tools as Everything Fonts can provide this conversion.
  • Limit the number of variants used or use a variable font
  • Load only the characters that are really used (for example via a subset)

When ?

These good practices must be implemented as soon as the visual design of the service is done in order to favor standard fonts as much as possible. If this is not possible, then limit the number of variants to be loaded. Finally, when fonts are integrated, use the woff2 format, variable fonts and make sure to load only the characters or languages actually used.

Ease of implementation

If the site is already online, it can be complicated to change the font used. On the other hand, technical optimizations are easy to implement (format, variable font, Subset).

Estimated gains

These best practices reduce the number of HTTP requests and the volume of data transferred.

Specific cases

Google Fonts

To avoid problems with the RGPD, it is recommended to host Google Fonts yourself.
If variable versions are not available for all, some creators offer these versions for free. In addition, the Google API allows you to directly create a Subset with a request of this type:


Icon fonts are quite common. Using them directly may imply loading many icons that will not necessarily be used. The best way to use icons is to use each of them directly in SVG format. In this form they can be embedded directly in the HTML (without any additional HTTP request). If an icon font must be kept for practical reasons, limit the file to the icons actually used.

Case study

As part of the support Docaposte teams receive for their corporate site, fonts are often a separate project.

The fonts used here are two Google Fonts: Montserrat and Barlow. The site being already online, it is complicated to impose the use of standard fonts.

To avoid violating the GDPR and to improve site performance, fonts are hosted directly on Docaposte’s servers. In a second phase, a dedicated subdomain could be set up to eliminate the need for cookies.

The integration in the form of a variable font requires some additional adjustments, especially in the style sheets. In the meantime, it was decided to apply two best practices:

  • Propose the files in woff2 format rather than woff
  • The site being proposed only in French and English, a Subset was created keeping only the Latin alphabet.

Original requests

Requests after Subset and conversion to woff2

The woff2 format offers an average of 30% more compression than the woff format and even more than other formats like ttf.

This change in format, combined with Subset, reduced the total weight of the fonts from just over 400 kb to just under 90 kb, a reduction of about 78%.

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