observablehq.com draws its body text in Source Serif 4. It uses 3 fonts in all. We measured it on November 4, 2026.
The fonts observablehq.com draws
| Font | Used for | Share of its custom-font text | Licence | How common |
|---|---|---|---|---|
| Source Serif 4 | Body text | 46.5% | Open source | 3 of 845 sites (rank =41) |
| Spline Sans Mono | Smaller text | 44.6% | Open source | – |
| Inter | Smaller text | 9% | Open source | 126 of 845 sites (rank 1) |
Share is how much of the page’s custom-font text each font draws. System fonts and icon fonts are never counted. Each site was opened twice in a real browser and Chrome was asked which font file drew each piece of text. We count a font for a site only if both runs saw it and it drew at least 2% of the site’s custom-font text. The full method.
Can I use the same fonts?
- Source Serif 4 is open source and free to use, including commercially. Get it from Google Fonts.
- Spline Sans Mono is open source and free to use, including commercially. Get it from Google Fonts.
- Inter is open source and free to use, including commercially. Get it from Google Fonts.
observablehq.com among developer tools and infrastructure sites
observablehq.com is one of the 89 developer tools and infrastructure sites we measured. Across them, Inter is the most used font you can get, on 31 of the 89 (35%). All the fonts developer tools and infrastructure sites use.
What pairing does observablehq.com use?
observablehq.com has no heading and body font pair to compare, because no single font clearly leads both. Pairings real sites use.
Other developer tools and infrastructure sites we measured
- algolia.com Sora, Inter
- angular.dev Inter, DM Mono
- astro.build Obviously, Inter, MD IO
- circleci.com Inter
- codesandbox.io Inter
- deno.com Inter
See the fonts on all 845 sites.
FAQ
What font does observablehq.com use?
observablehq.com draws its body text in Source Serif 4. It uses 3 fonts in all: Source Serif 4, Spline Sans Mono, Inter. We measured it on November 4, 2026.
Is Source Serif 4 free?
Yes. Source Serif 4 is open source and free for commercial use, according to Google Fonts.
What font pairing does observablehq.com use?
observablehq.com does not have a clear heading and body pair: no single font leads both.
Can I use the same fonts as observablehq.com on my own site?
Only if the licence allows it. Free and open-source fonts can be used freely. Commercial fonts need your own licence, even though you can see the file on observablehq.com. Each font's licence is on this page, from its source.
How do you know which font observablehq.com uses?
We opened observablehq.com in a real browser and asked Chrome which font file drew each piece of text, twice in separate sessions. A font counts only if both runs saw it and it drew at least 2% of the site's custom-font text.
Can I check a different website?
Yes. Paste its address into the free font finder.