Pretext is an open-source JavaScript library by Cheng Lou that measures and lays out multiline text without touching the DOM. Here is what it does, who built it, where it was published, how the community took it up, and what it is not. Including how it relates to our own website product, and how it does not.
9 min read · updated September 7, 2026 · every claim links to its source
Our website product is called Think Bright Sites. For a few months during development it carried the working name "preText," chosen as a nod to the library and the idea behind it: measure first, then decide. We retired that name before launch, for the reason this article makes obvious. A product should not share a name with a library it does not run, and Cheng Lou's work should not be confused with ours. We are not affiliated with him, and he has not endorsed us.
Where we use the library: inside the row editor that our team and clients use to change a page, so text edits reflow instantly without a browser layout hit. Where we plan to use it: the preview thumbnails in the onboarding wizard, a pre-flight check that a headline will not wrap to four lines on a phone before we spend a screenshot on it, and the text-on-image work in the social asset builder.
Where we do not use it: the pages you receive. A Think Bright page is plain HTML. The browser lays out the text, and nothing runs in the page except the small script that makes forms work. That is deliberate. The library exists to avoid the browser's layout pass when you are drawing text yourself. When the browser is drawing the text, the right amount of JavaScript is none.
So the honest sentence is this. Pretext is a text measurement engine that a lot of people are excited about, for good reason. Think Bright Sites is a way to rebuild the website you already have, match first, and keep it as a file you own. One informed the other. They are not the same thing.
Paste your URL. We rebuild it, show you the match, and measure the speed. No template. No blank page. Human review from start to finish.
