font-subsetting-prompt.md asks a coding agent to make a site's web fonts load faster without changing how anything looks: measure the fonts, audit what the site uses, subset each font, split it into a preloaded core file and an extended file behind unicode-range, and prove the result with before and after pixel diffs.
It is a rewrite of a 25-sentence prompt that worked in an earlier project. Every original sentence is still in it (see the coverage map), restructured along Anthropic's prompting guides for Claude Opus 5.5.
- Paste
font-subsetting-prompt.mdinto Claude Code at the repository root. - Fill in `` with the framework, where the fonts and
@font-facerules live, and the build and production-like serve commands, or delete the block and let the agent find them.