Frontend Performance25-45 min
Font Loading Optimization
Self-host important fonts, preload only critical font files, use `font-display`, and tune fallback metrics to prevent visible jumps.
CSSGoogle FontsNext.jsHTML
Prerequisites
- A page using custom web fonts.
- Access to font files or font provider settings.
- A before/after CLS measurement.
1
Plan the implementation
Start by choosing the exact page, route, API, or deployment surface you want to improve. A narrow target makes the implementation measurable and easier to verify.
- Write down the current behavior and the user-facing problem it creates.
- Pick one measurable success signal such as bundle size, latency, error rate, security coverage, or UI responsiveness.
- Identify the files, routes, providers, and environment variables involved.
- Create a rollback note before changing production-sensitive configuration.
2
Set up the required tools
Install or configure only the tools needed for this implementation. Keep config close to the feature so future developers can find the moving parts quickly.
Implementation snippet
npm run preview
# DevTools > Network > filter by Font.Checklist
- Dependencies are added to the correct workspace package.
- Environment variables are documented in `.env.example` when needed.
- Local development still starts without production-only secrets.
- The change is small enough to review in one pull request.
3
Implement the core pattern
- Audit which font weights and styles are actually used.
- Remove unused weights and icon-font files.
- Self-host or use framework font optimization when appropriate.
- Preload only the critical above-the-fold font file.
- Use `font-display: swap` or another intentional display strategy.
Implementation snippet
@font-face {
font-family: "Inter";
src: url("/fonts/inter-var.woff2") format("woff2");
font-display: swap;
}
body { font-family: Inter, Arial, sans-serif; }4
Handle edge cases
Checklist
- No unused font weights are downloaded on first load.
- Text remains visible while fonts load.
- Fallback font metrics do not cause major layout shift.
- Font files are cached with long-lived headers.
5
Verify before production
- Run the app locally and test the normal success path.
- Test one failure path, one empty state, and one slow-network or retry path.
- Run the project build and any related unit or integration tests.
- Check browser console, server logs, and network responses for hidden warnings.
- Document the final behavior, commands used, and any follow-up work.