bundle-pulse

bundle-pulse

A CI gate for JavaScript and CSS bundle size: budgets on raw, gzip and brotli sizes, and a diff against your base branch.

Bundles grow one innocent import at a time. bundle-pulse measures every JS and CSS file in your build output the way browsers receive it (gzip and brotli as well as raw), checks each file against the budget for its glob, checks total JS and CSS, and compares against a snapshot from the base branch so a pull request that adds 40 kB to the main chunk fails with a clear message. Content hashes in file names (index-BdT9x2Qa.js, main.3f2a9c1b.chunk.js) are stripped when comparing, so the diff follows the entry, not the file name.

CLI, library and GitHub Action. Node.js 18+, zero runtime dependencies, runs offline. By Louis Wright.

Features

• Three sizes: raw, gzip (level 9) and brotli (quality 11) for every .js, .mjs, .cjs and .css file; source maps are skipped.
• Budgets: per-glob budgets on any of the three sizes, total JS and total CSS budgets, and a warning when a file passes 90% of its budget.
• Base diff: --snapshot writes sizes to JSON; --base compares against it and reports files that grew more than --max-growth percent (default 10%, ignoring changes under 1 kB) and new large chunks.
• Hygiene: unminified files, identical files shipped under two names, budgets that match nothing (renamed entries), and large files with no budget.
• Works with any bundler: Vite, webpack, Rollup, esbuild, Parcel, Next.js static output, or plain files.

Scope

bundle-pulse measures what is on disk after the build. It does not analyse which modules are inside a chunk (use a bundle analyser for that) or measure runtime performance (see vitals-pulse).

Rules

Install and run

npx bundle-pulse dist
npx bundle-pulse dist -b 'assets/index-*.js=60KB' -b 'assets/*.css=brotli:15KB' --total-js 200KB
npx bundle-pulse dist --snapshot bundle-base.json   # on main
npx bundle-pulse dist --base bundle-base.json --max-growth 5 --format markdown

Sample output

bundle-pulse — test/fixtures/bad
5 file(s): JS 32.6 kB gzip, CSS 10.9 kB gzip

HIGH     Total JS is 32.6 kB gzip, over the 30.0 kB budget [bundle-total-over-budget]
HIGH     test/fixtures/bad/assets/app-K2m9xQ7r.css assets/app-K2m9xQ7r.css is 10.9 kB gzip, over its 6.0 kB budget by 4.9 kB (82%) [bundle-over-budget]
HIGH     test/fixtures/bad/assets/index-Xa91bQ2k.js assets/index-Xa91bQ2k.js is 9.1 kB gzip, over its 8.0 kB budget by 1.1 kB (14%) [bundle-over-budget]
MEDIUM   Budget "assets/admin-*.js" matches no file [bundle-budget-unmatched]
MEDIUM   test/fixtures/bad/assets/legacy.js assets/legacy.js (40.0 kB) looks unminified [bundle-unminified]

Options

bundle-pulse 1.0.0 — JS/CSS bundle size budgets with raw, gzip and brotli sizes

Usage: bundle-pulse [build-dir] [options]

Budgets
  -b, --budget <glob=size>  Budget for matching files, repeatable; gzip by default ("assets/index-*.js=60KB",
                            "**/*.css=brotli:20KB", "vendor*.js=raw:400KB")
      --total-js <size>     Budget for all JS together (gzip)
      --total-css <size>    Budget for all CSS together (gzip)
      --include <globs>     Files to measure (default **/*.{js,mjs,cjs,css}; source maps always skipped)
      --exclude <globs>     Files to skip
Base comparison
      --base <file>         Snapshot from the base branch (written with --snapshot)
      --base-optional       Do not fail if the base snapshot does not exist yet
      --max-growth <pct>    Allowed growth per file vs base, in percent (default 10)
      --snapshot <file>     Write the current sizes as a snapshot

Common
  -c, --config <file>     JSON config (default: .bundle-pulse.json or "bundlePulse" 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 .bundle-pulse.json (or a "bundlePulse" key in package.json, or --config <file>):

{
  "failOn": "medium",
  "severity": {
    "bundle-over-budget": "low"
  },
  "allowlist": [
    {
      "rule": "bundle-unminified",
      "subject": "assets/legacy.js",
      "reason": "Vendored legacy widget, replaced in Q1",
      "expires": "2027-03-31"
    }
  ],
  "budgets": [
    {
      "path": "assets/index-*.js",
      "gzip": "60 KB",
      "brotli": "50 KB"
    },
    {
      "path": "assets/*.css",
      "gzip": "15 KB"
    }
  ],
  "totalJs": "200 KB",
  "maxGrowth": 5,
  "base": "bundle-base.json"
}

• 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).

The config file is looked up in the target directory first, then in the current directory, so .bundle-pulse.json can live at your repository root. Other keys: budgets (array of { path, raw, gzip, brotli } or a map of glob to gzip size), totalJs, totalCss, maxGrowth, warnAt (percent, default 90), minDelta, largeFile, newLarge, base, include and exclude. The config file is read from the build directory or from --config.

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:
  bundle-pulse:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
        with: { persist-credentials: false }
      - uses: MrLouisWright/bundle-pulse@v1
        with:
          path: dist
          fail-on: high
          sarif: bundle-pulse.sarif
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with: { sarif_file: bundle-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 { scan, analyze, normaliseBudgets } from "bundle-pulse";
const files = scan("dist");
const findings = analyze(files, { budgets: normaliseBudgets({ "assets/index-*.js": "60 KB" }) });

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 bundle-pulse helps you, a link back is appreciated:

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

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

Licence

MIT © Louis Wright (Louis Wright)