Simon Willison’s Weblog

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29th March 2026

Tool Pretext — Under the Hood — Explore how pure-JavaScript text measurement and line breaking work through an interactive visualization of the Pretext library's pipeline. This tool demonstrates each stage from raw text input through whitespace normalization, word segmentation, canvas-based width measurement, and arithmetic-based line breaking, with live verification against actual DOM rendering.

See my notes on Pretext here.

Posted 29th March 2026 at 7:59 pm

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