The brand typeface, what the app actually renders, and why you can't set a font on a tweet.
Twitter, now X, uses Chirp as its brand typeface. Chirp launched in 2021 as the platform's first custom font and is used across branding and much of the interface chrome.
But inside the app itself, most body and tweet text is drawn with the device's default system fonts — San Francisco on iOS, Roboto on Android, and the platform default on the web. So the honest answer is two-part: the brand is Chirp; the words in your feed are usually system fonts.
No. Chirp is X's proprietary brand typeface, commissioned for the company, and is not released as a public download for general design use.
Designers who want a similar feel usually reach for a clean grotesque or humanist sans-serif, but there is no official public Chirp package to install.
X's font choices (Chirp for the brand, system fonts for content) are separate from the “fancy fonts” people paste into tweets and bios. Those styled letters are Unicode characters — bold, italic, script, and similar variants that live in the text itself.
That is why the styling survives when the text is copied elsewhere, and why you can do it on any account without a setting. There is no menu to switch a tweet's font; you paste characters that already look styled.
Generate Unicode styles for tweets, display names, and bios in one click, then paste them straight into X.
Style your X text →