font-pulse

font-pulse

Audit how your built site loads web fonts: font-display, preloads, WOFF2, subsetting, unused weights and total font payload.

Web fonts are a quiet source of slow text and layout shift: a missing font-display hides text for up to three seconds, a preload without crossorigin downloads the font twice, and a design system that ships nine weights when the pages use two costs hundreds of kilobytes. font-pulse reads the HTML and CSS in your static build output, follows linked stylesheets and @import, and checks every @font-face against how the site actually uses it.

CLI, library and GitHub Action. Node.js 18+, zero runtime dependencies. Works on any static build output (Astro, Next.js output: 'export', Eleventy, Hugo, Jekyll, Docusaurus, VitePress, plain HTML) and runs offline: point it at the folder your build writes. By Louis Wright.

Features

• Loading: font-display missing or block/auto; Google Fonts URLs without display=swap; third-party font hosts without preconnect.
• Preloads: self-hosted fonts with no preload, preloads without crossorigin (double download), preloads of files no @font-face uses, and too many font preloads.
• Formats and size: @font-face without a WOFF2 source, font files over 100 kB (subset them), large fonts without unicode-range.
• Waste: families declared but never used in font-family, weights and italic faces never used (headings and <strong> count as bold), more than six font files per page, and a per-page payload budget (default 300 kB).
• Understands real CSS: the font shorthand, CSS custom properties, variable-font weight ranges, @import chains and inline styles.

Scope

font-pulse works from your build output and file sizes on disk; it does not render pages, so "unused" means not referenced by any CSS or default bold element. It does not check cache headers for font files (see cache-pulse) or broken font URLs (static-link-sentinel).

Rules

Install and run

npx font-pulse dist
npx font-pulse public --max-payload-kb 200 --fail-on medium
npx font-pulse _site --format markdown >> $GITHUB_STEP_SUMMARY

Pages are mapped to URLs the way static hosts serve them: index.html → /, blog/index.html → /blog/, about.html → /about.html (or /about with --clean-urls). Pass --base-url with your public URL, or let it be inferred from canonical / og:url tags. Meta-refresh redirect stubs and 404.html are skipped. X-Robots-Tag and Link headers are read from Netlify/Cloudflare _headers and vercel.json.

Sample output

font-pulse — /workspace/font-pulse/test/fixtures/bad
1 page(s), 1 with web fonts, 4 font file(s)

MEDIUM   css/fonts.css:2 @font-face "brand" has no font-display [font-display-missing]
MEDIUM   css/fonts.css:2 @font-face "brand" offers woff, ttf but no WOFF2 [font-no-woff2]
MEDIUM   css/fonts.css:2 fonts/brand.woff is 88 KB [font-heavy]
MEDIUM   css/fonts.css:3 @font-face "brand" uses font-display: block [font-display-missing]
MEDIUM   index.html / declares 3 font file(s) totalling 195 KB (budget 150 KB) [font-payload]
MEDIUM   index.html:2 /: <link rel="preload" href="/fonts/brand.woff"> has no crossorigin [font-preload-no-crossorigin]

Options

font-pulse 1.0.0 — audit web font loading in your built site

Usage: font-pulse [site-dir] [options]

Site
      --base-url <url>        Public URL of the site, e.g. https://example.com (default: inferred from canonical/og:url)
      --include <globs>       Only check these pages (file or URL path globs, comma-separated)
      --exclude <globs>       Skip these pages
      --clean-urls            Pages are served without .html (about.html -> /about)
Fonts
      --max-payload-kb <n>     Font budget per page in KB (default 300)
      --max-file-kb <n>        Size above which a font file should be subset, in KB (default 100)

Common
  -c, --config <file>     JSON config (default: .font-pulse.json or "fontPulse" in package.json)
  -f, --format <fmt>      text (default) | json | sarif | markdown
      --json <file>       Also write a JSON report
      --sarif <file>      Also write SARIF 2.1.0
      --markdown <file>   Also write Markdown (e.g. for a job summary)
      --fail-on <sev>     critical | high | medium | low | info | none (default: high)
      --list-rules        Print rules and default severities
      --no-fixes          Hide fix suggestions in text output
      --no-color          Disable colours
  -v, --version / -h, --help

Exit codes: 0 = passed, 1 = findings at or above --fail-on, 2 = usage, config or read error.

Configuration and allowlist

Options can live in .font-pulse.json (or a "fontPulse" key in package.json, or --config <file>):

{
  "failOn": "medium",
  "severity": {
    "font-display-missing": "low"
  },
  "allowlist": [
    {
      "rule": "font-heavy",
      "subject": "fonts/noto-sans-jp.woff2",
      "reason": "CJK font, already split by unicode-range on the CDN",
      "expires": "2027-03-31"
    }
  ],
  "maxPayload": 204800,
  "maxFile": 81920,
  "maxFaces": 4,
  "maxPreloads": 2,
  "requirePreload": true
}

• severity changes a rule's severity, or turns it "off".
• allowlist entries suppress matching findings. Each needs a reason and matches on any combination of rule, file, subject (globs with *) and match (a substring of the message). Add expires (YYYY-MM-DD) so the exception is time-boxed: once it lapses the finding comes back along with an allowlist-expired finding (medium). Entries that no longer match anything are reported as allowlist-unused (info).

Config can also set baseUrl, include, exclude and cleanUrls. The config file is looked up in the site directory first, then in the current directory, so .font-pulse.json can live at your repository root. Other keys: maxPayload, maxFile, maxFaces (default 6), maxPreloads (default 3), requirePreload (default true), plus baseUrl, include, exclude and cleanUrls.

Output and exit codes

• --format text (default), json, sarif (SARIF 2.1.0 for GitHub code scanning) or markdown (for job summaries and PR comments). --json, --sarif and --markdown write extra report files in the same run.
• --fail-on <severity> sets the threshold (critical, high, medium, low, info, none; default high).
• Exit codes: 0 passed, 1 findings at or above --fail-on, 2 usage, config or read error.

GitHub Action

permissions:
  contents: read
  security-events: write   # only needed for the SARIF upload
jobs:
  font-pulse:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
        with: { persist-credentials: false }
      - run: npm ci && npm run build   # produce the static site first
      - uses: MrLouisWright/font-pulse@v1
        with:
          path: dist
          fail-on: high
          sarif: font-pulse.sarif
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with: { sarif_file: font-pulse.sarif }

The action runs the bundled CLI with Node 20; it has no dependencies to install. Pin it to a commit SHA if your policy requires it.

Library

import { check, parseCss } from "font-pulse";
parseCss("@font-face{font-family:Inter;src:url(i.woff2) format('woff2')}").faces;
const report = check("dist", { maxPayload: 200 * 1024 });

Types are included.

Requirements

Node.js 18 or newer. Zero runtime dependencies.

Support

If this project is useful to you, you can support its development with a donation: Buy me a coffee. It helps keep these tools maintained, documented and free for everyone.

Credit (optional)

Free to use under MIT, no attribution required. If font-pulse helps you, a link back is appreciated:

<a href="https://louiswright.co.uk">Built with font-pulse by Louis Wright</a>

[![Built with font-pulse by Louis Wright](https://img.shields.io/badge/built%20with-font--pulse-blue)](https://louiswright.co.uk)

Licence

MIT © Louis Wright (Louis Wright)