HTML Input

Forme 0.14 adds a second front door to the engine: @formepdf/html renders HTML + print CSS to PDF through the same Rust/WASM engine that renders JSX components. No headless browser, no Chromium cold start.

# CLI — zero config
npx @formepdf/html invoice.html -o invoice.pdf

# with a separate stylesheet, page setup, and fonts
npx @formepdf/html report.html --css print.css --page-size Letter --margin 36 --font "Inter=Inter.ttf"

// Library
import { renderHtml } from "@formepdf/html";

const { pdf, warnings } = await renderHtml(html, { css, fonts });

The subset — the constitution

This is a deliberately documented subset of HTML/CSS, in the spirit of Satori — but page-native. Everything supported is listed below and tested. Everything outside the subset lands in the warnings list at render time, named, with a remedy where one exists. Nothing fails silently.

Paged media — the point of the whole thing

Supported	Not supported (warned)
`@page` `size` (named, dimensions, `landscape`) and `margin`	`@page` `bleed` / `marks`
`@page :first` — different margins, headers off the title page
`@page :left` / `:right` — mirrored margins (left + right must sum equally with the base `@page`; unequal sums warn and normalize to the base), per-side margin boxes on edges the base `@page` also defines. Page 1 is a `:right` page (LTR page progression; `dir="rtl"` parity is not modeled — warned). `:first` outranks parity on page 1	Per-side top/bottom margins (warned, normalized)
Named pages — `@page <name>` + `page: <name>`. The named run starts at a forced break, so top/bottom margins are real (a zero-margin cover works); left/right follow the mirrored-sum rule. Named margin boxes override/suppress the base running headers per name. Composes with `:first`/`:left`/`:right` (`@page cover:first`); named outranks `:first` outranks parity, per spec specificity	`:blank`, `:nth()` page groups, `string-set`/`content: string()`, `position: running()`, footnotes — warned by name
Margin boxes (`@top-center`, `@bottom-right`, …) for running headers/footers
Page counters — `counter(page)` and `counter(pages)`
`break-before` / `break-after` / `break-inside: avoid` (+ legacy `page-break-*` aliases)
`orphans` / `widows`
`@media` media-type evaluation — `print` is the native media type; feature queries evaluate against the page content box	`prefers-color-scheme`, `not` conditions (excluded with a named warning)
`<thead>` repetition across page breaks; table-cell overflow preservation

Elements

Supported	Not supported
Block containers: `div`, `section`, `article`, `header`, `footer`, `main`, `aside`, `nav`, `address`, `figure`, `blockquote`, `hr`	JavaScript of any kind (`<script>` skipped)
`h1`–`h6`, `p`, `br`	`<canvas>`, `<video>`, `<audio>`, `<iframe>`, forms
Inline: `span`, `b`/`strong`, `i`/`em`, `u`, `s`/`del`, `a`, `small`, `code`, `mark`, `sub`, `sup`	Inline `<img>` mid-paragraph
Tables: `table`, `thead`, `tbody`, `tfoot`, `tr`, `td`, `th` + `colspan`/`rowspan`
Lists: `ul`, `ol` (+ `start`), `li`
`img` (block-level) — data URIs and local files	External `http(s)` image fetching
`<style>` blocks; the CLI inlines local `<link rel="stylesheet">`	Remote stylesheets — never fetched, warned with the href and remedy

Selectors

Supported	Not supported (selector skipped, warned)
Type, class, id, universal; compounds	Pseudo-elements (`::before`, `::after`)
Attribute selectors — all seven operators (`[checked]`, `[type=text]`, `[class~=well]`, `[lang\|=en]`, `[href^="https:"]`, `[src$=".png"]`, `[class*="span"]`) + the `i` case flag	Sibling combinators (`+`, `~`); namespaced attribute selectors
Descendant and child combinators; grouping
`:first-child`, `:last-child`, `:nth-child(even\|odd\|an+b)`	`:only-child` and remaining tree pseudo-classes
`:first-of-type`, `:last-of-type`, `:nth-of-type`, `:nth-last-child`, `:nth-last-of-type`	Interaction pseudo-classes (`:hover`) — permanent: print has no hover
Full cascade with `!important`

Properties

CSS Grid is supported as a documented subset (not all of grid): fr/px/auto/minmax tracks, integer repeat() — including Tailwind’s repeat(N, minmax(0, 1fr)) — gaps, spans, and numeric line placement; named lines, areas, auto-flow, auto-fill/fit, percentage tracks, and negative line numbers warn by name. The full property table lives in the package README — margins with CSS margin collapsing, borders (solid/dashed/dotted with Chrome-matched dash metrics), border-collapse emulation, min/max width constraints (the centered-column idiom works), font fallback chains, text-align: justify with real Knuth-Plass distribution, text-transform, letter-spacing, vertical-align on cells, flexbox, relative/absolute positioning, floats as column rows (float: left/right + clear — consecutive floated siblings form a row, the Bootstrap col-* / left-right header-pair shape; text wrapping alongside a float is not supported and warns — following content renders below), CSS tables on divs (display: table/table-row/table-cell — the equal-height-columns idiom; a single-row one becomes a breakable column row), position: fixed as position: absolute by policy (anchored on the page where it occurs, not repeated per page — margin boxes are the running-content mechanism), and body { overflow-x: hidden } as a page-level clip (how off-viewport-parked sidebars stay invisible). Notable exclusions, all warned by name: CSS variables, position: sticky, transforms, gradients, @font-face fetching (use options.fonts / --font — see the web-fonts migration recipe).

The warnings contract

$ npx @formepdf/html letterhead.html -o letterhead.pdf
warning: unsupported property: text-transform-origin

Every warning names the thing it skipped: the property, the selector, the stylesheet href, the @font-face family. If a render is silent, the document used only the subset — and what you got is what the subset defines.

Browser, Workers, and edge

The HTML path ships web-target builds alongside Node (since 0.15.0), verified in real headless Chromium and real workerd:

// Bundlers / browser
import { renderHtml } from "@formepdf/html/browser";

// Cloudflare Workers / edge — WASM must be initialized explicitly
import { init, renderHtml } from "@formepdf/html/worker";
import wasm from "@formepdf/html/pkg-web/forme_pdf_html_bg.wasm";

await init(wasm); // idempotent — warm isolates skip it
const { pdf, warnings } = renderHtml(html);

Sizing: the HTML engine WASM is 7.66 MB uncompressed, 3.41 MB gzipped (measured from the published 0.20.0 package; the CI-measured figure lives in the parity artifact). Size is no longer the Workers constraint — Cloudflare raised the limit to 64 MiB uncompressed on all plans (2026-09-04), so the module fits the free plan. The real constraint is CPU time: the free plan caps at 10 ms per request and a typical render is ~20 ms (measured in workerd, local Apple Silicon, 0.20.0), so real workloads need the paid plan. The module compiles and instantiates in ~1 ms in a Workers isolate, so its size is a disk/transfer cost, not a cold-start cost. Mind the Workers 128MB memory ceiling, though: table-heavy documents render comfortably up to ~50 pages and approach the limit near ~100 pages (details).

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The subset — the constitution

Paged media — the point of the whole thing

Elements

Selectors

Properties

The warnings contract

Browser, Workers, and edge

Migrating

​The subset — the constitution

​Paged media — the point of the whole thing

​Elements

​Selectors

​Properties

​The warnings contract

​Browser, Workers, and edge

​Migrating

The subset — the constitution

Paged media — the point of the whole thing

Elements

Selectors

Properties

The warnings contract

Browser, Workers, and edge

Migrating