pretext

A workflow for building single-file browser demos with `@chenglou/pretext`, a small library that measures and lays out multiline text without changing the page layout. It provides line breaks, widths, character positions, and total height.

In plain words
What is it for?
Use it for text flowing around moving shapes, ASCII art made from real words, text-based games, kinetic typography, particle effects, and compact browser demos.
Why use it?
It avoids repeated browser layout calculations when text must move, wrap, or interact with objects. This makes precise text-based effects and layouts easier to build.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/john-data-chen/hermes-agent-backup/pretext
Any agent
npx skills add john-data-chen/hermes-agent-backup --skill pretext
Clone the repo
git clone --depth 1 https://github.com/john-data-chen/hermes-agent-backup

Made for: Claude Code, Codex.

Per session 56 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,512 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 92% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00056 $0.03512
Opus 5 $0.00028 $0.01756
Sonnet 5 $0.00011 $0.00702
Haiku 4.5 $0.00006 $0.00351

Measured yesterday against content hash 532570c95d1a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

pretext scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

92% identical to pretext — 8 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/creative/pretext/SKILL.md · 221 lines

How it starts

The opening of the file, as written. The whole thing — 221 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Pretext Creative Demos

Overview

@chenglou/pretext is a 15KB zero-dependency TypeScript library by Cheng Lou (React core, ReasonML, Midjourney) for DOM-free multiline text measurement and layout. It does one thing: given (text, font, width), return the line breaks, per-line widths, per-grapheme positions, and total height — all via canvas measurement, no reflow.

That sounds like plumbing. It is not. Because it is fast and geometric, it is a creative primitive: you can reflow paragraphs around a moving sprite at 60fps, build games whose level geometry is made of real words, drive ASCII logos through prose, shatter text into particles with exact per-grapheme starting positions, or pack shrink-wrapped multiline UI without any getBoundingClientRect thrash.

This skill exists so Hermes can make cool demos with it — the kind people post to X. See pretext.cool and chenglou.me/pretext for the community demo corpus.

When to Use

Use when the user asks for:

  • A "pretext demo" / "cool pretext thing" / "text-as-X"
  • Text flowing around a moving shape (hero sections, editorial layouts, animated long-form pages)
  • ASCII-art effects using real words or prose, not monospace rasters
  • Games where the playfield / obstacles / bricks are made of text (Tetris-from-letters, Breakout-of-prose)
  • Kinetic typography with per-glyph physics (shatter, scatter, flock, flow)
  • Typographic generative art, especially with non-Latin scripts or mixed scripts
  • Multiline "shrink-wrap" UI (smallest container width that still fits the text)
  • Anything that would require knowing line breaks before rendering

Don't use for:

  • Static SVG/HTML pages where CSS already solves layout — just use CSS
  • Rich text editors, general inline formatting engines (pretext is intentionally narrow)
  • Image → text (use ascii-art / ascii-video skills)
  • Pure canvas generative art with no text role — use p5js

Creative Standard

This is visual art rendered in a browser. Pretext returns numbers; you draw the thing.

Read the full file on GitHub · 221 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 221 lines · 56 tokens per session scan A 532570c95d1a

Subscribe to this mod's changes

pretext is a skill published in the GitHub repository john-data-chen/hermes-agent-backup (2 stars, last pushed 1mo ago), licensed MIT. It adds 56 tokens to every session and 3,512 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 92% identical to pretext, differing in 8 lines, and is treated as a copy.

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