budget: page weight and images

budget adds up what each built page references and fails when a page, its HTML, CSS or JavaScript, or a single image grows past a limit. It also warns about large PNG, JPEG and GIF files served without a modern alternative, and about images without dimensions that shift the layout while they load. Weight creeps up one dependency or hero image at a time; a budget in CI catches the commit that crosses the line. It is not in the default set.

Needs

Nothing to install. It reads the build (dist/) and starts no server or browser, so it measures files, not network transfers.

Run it

npx vidimus budget

What it checks

Pages matched by the top-level exclude or budget.exclude are skipped.

What counts

Only files in the build count; URLs on other origins are ignored, and absolute URLs on siteUrl are resolved to the build. Each file counts once per page, however often the page references it.

Kind	Files	Measured
html	the page itself	gzipped
css	<link rel="stylesheet">	gzipped
js	<script src> and <link rel="modulepreload">	gzipped
images	<img src>, srcset of <img> and <source>	raw bytes
page	all of the above	sum of the sizes above

Not counted: iframes and what they load (Lighthouse counts them), fonts, CSS background images, <video>/<audio> sources, and anything a script or stylesheet loads, unless render.mode is on. With rendering, html is still the shipped file, and the other kinds are the build files the browser requested while rendering: stylesheets, scripts (lazy chunks included) and images by request type, while fonts, media and fetch requests (models, data) count toward page only. Every candidate in a srcset counts toward the page total, not only the one a browser would pick, so pages with many responsive variants read heavier than a real visit.

Checks

• Per-page budgets (budget.html, budget.css, budget.js, budget.page): a page over a limit fails with <kind> <size> gzipped > <limit> budget (or total for page), listing the three largest files of that kind as detail.
• Image size (budget.image): any referenced image over the limit fails with image <path> <size> > <limit> budget, once per image, listing every page that uses it.
• Legacy formats (budget.legacyImage): an <img> whose src or srcset has a .png, .jpg, .jpeg or .gif file larger than the limit warns with image <path> is <size>: serve AVIF or WebP, unless the <img> sits inside a <picture> with a <source> that has type="image/avif" or type="image/webp", or .avif or .webp files in its srcset.
• Dimensions (budget.dimensions): an <img> without both width and height warns with <img src="…"> has no width and height (layout shift). Images with a data: URL and images with aspect-ratio in their inline style are exempt. When vidimus can read the image’s intrinsic size (PNG, JPEG, GIF, WebP, AVIF, and SVG with width/height or viewBox), the fix includes the exact attributes to add.

Sizes are shown in decimal units: B below 1000 bytes, kB, then MB. A limit of 0 turns that check off. The summary names the heaviest page.

Example output

─── budget ──────────────────────────────────────────────────────

✖ js 312 kB gzipped > 250 kB budget
    188 kB /_astro/charts.B3kx9.js
    96 kB /_astro/client.Dq1fa.js
    28 kB /_astro/page.Ce72b.js
    in: dist/dashboard/index.html
    on: /dashboard/
    → Split or lazy-load the largest scripts listed above, drop unused dependencies, or raise budget.js.

✖ image /img/team.jpg 1.4 MB > 500 kB budget
    in: dist/img/team.jpg
    on: /about/ /it/chi-siamo/
    → Resize/compress it (e.g. with sharp or squoosh) and serve AVIF/WebP, or raise budget.image.

⚠ image /img/team.jpg is 1.4 MB: serve AVIF or WebP
    in: dist/img/team.jpg
    on: /about/ /it/chi-siamo/
    → Add a <picture> with a <source type="image/avif"> or <source type="image/webp"> before this <img>.

⚠ <img src="/img/logo.png"> has no width and height (layout shift)
    on: / /about/ /blog/ +12 more
    → Add width and height attributes matching the image's intrinsic size, e.g. width="240" height="64" (CSS can still resize it).

✖ budget: 15 page(s), heaviest /about/ 1.6 MB, 4 problem(s) (0.2s)

Options

Key	Default	Description
budget.html	100_000	max gzipped bytes of a page’s HTML
budget.css	100_000	max gzipped bytes of a page’s stylesheets
budget.js	250_000	max gzipped bytes of a page’s scripts, including modulepreload
budget.page	2_000_000	max total bytes per page
budget.image	500_000	max bytes of any image in <img>, srcset or <source>
budget.legacyImage	100_000	warn when a PNG/JPEG/GIF this large has no AVIF/WebP <source>
budget.dimensions	true	warn on <img> without width and height
budget.exclude	[]	URL path patterns to skip

0 turns any of the byte limits off.

import { defineConfig } from 'vidimus';

export default defineConfig({
  audits: ['i18n', 'csp', 'a11y', 'links', 'r12s', 'budget'],
  budget: {
    js: 150_000,
    page: 1_000_000,
    legacyImage: 0,
    exclude: ['^/playground/'],
  },
});

From the command line: npx vidimus budget --set budget.js=150000.

Common fixes

Add the intrinsic size to every <img>. The browser reserves the space from the ratio, and CSS can still scale it:

<img src="/img/logo.png" alt="Example" width="240" height="64">

img {
  max-width: 100%;
  height: auto;
}

When the size is not known at build time (images from a CMS), set a ratio instead:

<img src="/uploads/cover.jpg" alt="" style="aspect-ratio: 16 / 9; width: 100%">

Serve a modern format with a fallback. budget is satisfied as soon as the <picture> has an AVIF or WebP <source>:

<picture>
  <source type="image/avif" srcset="/img/team.avif">
  <source type="image/webp" srcset="/img/team.webp">
  <img src="/img/team.jpg" alt="The team" width="1600" height="900">
</picture>

Most frameworks generate this for you: <Picture> in astro:assets, @11ty/eleventy-img, Hugo image processing. Convert existing files with sharp:

node -e "require('sharp')('public/img/team.jpg').avif().toFile('public/img/team.avif')"

For JavaScript over budget, the three largest files in the finding are where to start: import heavy libraries (charts, editors, maps) dynamically on the pages that need them, and check for duplicates of the same dependency. For HTML over budget, look for inlined SVG sprites, large inline JSON (hydration state) and long lists that could be paginated.