Pretext Text Metrics — guide skill for captions & subtitles

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Measure and fit text without the DOM using pretext: auto-fit sizes, know line breaks before render, canvas/WebGL text.

• Type: Guide · Captions & subtitles
• Slug: pretext-yaniv-golan
• Status: beta
• Publisher: Yaniv Golan (community)
• License: MIT
• Source: https://github.com/yaniv-golan/pretext-skill/tree/main/pretext/skills/pretext
• Works in: Claude Code, Claude.ai, Codex, Cursor, ChatGPT
• Requires: @chenglou/pretext from npm, A browser or OffscreenCanvas with Intl.Segmenter (in Node, node-canvas works but accuracy is not guaranteed)
• Cost: Free — open-source, runs locally
• Adoption: 19 installs, 15 GitHub stars (skills.sh, 2026-10-26)

What it does

Teaches agents to use @chenglou/pretext, a small library that measures and lays out text with canvas math instead of DOM reflow. It covers the core and rich-inline APIs and the bugs that bite: lineHeight in pixels rather than a multiplier, text-then-font argument order, measuring only after web fonts load, unreliable system-ui, letterSpacing in pixels, and measuring the exact string that will be rendered. Patterns include auto-fitting a font size to a box, height estimation, text flowing around obstacles and shrink-wrapped bubbles, which is what titles drawn in canvas or WebGL compositions need. It tracks pretext 0.0.8, while npm's latest is 1.0.0 (2026-10-14), so check for API drift.

Use when

• Auto-fit a font size so a title fits a box or N lines
• Know line count and height before rendering text
• Flow text around shapes or across variable-width lines
• Measure text for canvas, SVG or WebGL rendering

Not for

• CSS-only text layout or generic typography advice (the skill's own exclusion)
• Structured HTML content: pretext measures plain text strings

Install

• Claude Code: /plugin marketplace add yaniv-golan/pretext-skill && /plugin install pretext@pretext-marketplace
• Codex: $skill-installer https://github.com/yaniv-golan/pretext-skill
• Cursor: npx skills add yaniv-golan/pretext-skill

More captions & subtitles skills

• 3D Camera Captions: Captions that live in 3D around a talking head: the camera flies through the words, heroes pass behind the speaker.
• Remotion Captions: Transcribe speech and burn in animated captions with Remotion, or import an existing SRT file.
• ElevenLabs Speech to Text: Transcribe audio and video with word timestamps, speaker labels and keyterms, ready for subtitles.
• ElevenLabs Speech to Text (inference.sh): Transcribe audio with ElevenLabs Scribe, speaker diarization and forced alignment, via inference.sh.
• Speech to Text: Transcribe audio with ElevenLabs Scribe v2 or Whisper V3 Large, with timestamps and speaker labels.
• Chinese Font Selector: Pick Chinese fonts by license tier first (OFL, vendor-free, avoid), then by scene and mood, with Latin pairings.