@slothpdf/render

Fast PDF generation from templates. 17,000+ PDFs per second. No headless browser.

Built on a native engine written in Zig. No Puppeteer, no Chrome, no runtime overhead. Constant memory.

Install

bun add @slothpdf/render

Requires Bun v1.1+. The correct native binary is installed automatically.

Quick start

import { render } from "@slothpdf/render";

const pdf = render(`
  <Page size="A4" margin="20mm">
    <Box class="text-2xl font-bold mb-4">Hello, {name}!</Box>
    <Box class="text-sm text-gray-600">{description}</Box>
  </Page>
`, { name: "World", description: "Generated with SlothPDF" });

await Bun.write("hello.pdf", pdf);

Batch

Pass an array and render yields one PDF per row:

for (const { index, buffer } of render(template, invoices)) {
  await Bun.write(`invoices/${index}.pdf`, buffer);
}

Merge

All rows into a single multi-page PDF:

await Bun.write("report.pdf", render(template, rows, { merge: true }));

ZIP

All rows as a ZIP archive:

await Bun.write("invoices.zip", render(template, rows, { zip: true }));

Encryption

AES-256 password protection:

await Bun.write("secure.pdf", render(template, data, { password: "secret" }));

Works with all modes — single, merge, zip, compress.

Init

Preload fonts and images at startup. Skips assets already loaded.

import { init, render } from "@slothpdf/render";

init({
  fonts: {
    Inter: { regular: "fonts/Inter-Regular.ttf", bold: "fonts/Inter-Bold.ttf" },
    Mono: "fonts/JetBrainsMono-Regular.ttf",
  },
  images: {
    logo: "assets/logo.png",
  },
});

Custom fonts

import { loadFont } from "@slothpdf/render";

loadFont("Inter", await Bun.file("Inter-Regular.ttf").bytes());
loadFont("Inter", await Bun.file("Inter-Bold.ttf").bytes(), "bold");

<Page size="A4" margin="20mm" font="Inter">
  <Box class="font-bold">This renders in Inter Bold</Box>
</Page>

Images

import { loadImage } from "@slothpdf/render";

loadImage("logo", await Bun.file("logo.png").bytes());

<Image src="logo" class="w-32" />

QR codes

<QrCode src="https://example.com/pay/inv-042" class="h-[120]" />

Page headers & footers

<Page size="A4" margin="20mm">
  <PageHeader class="flex-row border-b border-gray-200 pb-3">
    <Box class="text-lg font-bold">Acme Corp</Box>
    <Box class="text-right text-sm">Invoice #2026-042</Box>
  </PageHeader>

  <!-- page content -->

  <PageFooter class="flex-row border-t border-gray-200 pt-2 text-xs text-gray-400">
    <Box>hello@acme.com</Box>
    <Box class="text-right">Page {page}</Box>
  </PageFooter>
</Page>

Template syntax

Templates use an HTML-like markup with utility classes. If you've built a web page, the syntax will feel familiar.

Elements: Page, Box, Text, Image, QrCode, Line, Columns, Column, PageHeader, PageFooter

Layout: flex-row, flex-col, justify-between, items-center, gap-4

Sizing: w-1/2, w-full, h-16

Spacing: p-4, px-6, mt-2, mb-8

Typography: text-sm, text-2xl, font-bold, text-gray-500, text-center

Data: {field}, {nested.field}, each="arrayField", when="condition"

<Box each="items" class="flex-row py-2 border-b border-gray-100">
  <Box class="w-2/3 text-sm">{name}</Box>
  <Box class="w-1/3 text-sm text-right">{price}</Box>
</Box>

<Box when="discount" class="text-green-600">
  Discount applied: {discount}
</Box>

CLI

slothpdf render template.sloth data.json -o output.pdf
slothpdf batch template.sloth rows.json -o invoices/
slothpdf render template.sloth --font "Inter=Inter-Regular.ttf" --compress -o out.pdf

API reference

render(template, data?, options?)

The only function you need. Behavior depends on what you pass:

Call	Returns
render(template, object)	Buffer — single PDF
render(template, array)	Generator<{ index, buffer }> — one PDF per row
render(template, array, { merge: true })	Buffer — one multi-page PDF
render(template, array, { zip: true })	Buffer — ZIP archive

Options:

• compress boolean — FlateDecode compression (smaller files)
• password string — AES-256 encryption
• merge boolean — combine all rows into one PDF
• zip boolean — package all PDFs into a ZIP

All options are additive — { compress: true, password: "secret", merge: true } works.

init(options)

Preload fonts and images from file paths. Skips assets already loaded.

loadFont(name, ttf, variant?)

Register a TrueType font. Variant: "regular" | "bold" | "italic".

loadImage(key, data) · hasImage(key) · clearImages()

Register, check, or clear images for <Image src="key" />.

hasFont(name)

Check if a font family is loaded. Returns boolean.

Performance

Benchmarked on Apple M4, single-threaded, 1000 unique invoices with 3–10 line items:

Mode	Latency	Throughput
No encryption	0.057ms	17,600 /sec
AES-256 encrypted	0.067ms	14,900 /sec

Memory is constant after warmup — 50,000 renders with no growth.

Compared to other tools:

Tool	~Speed
SlothPDF	17,600 /sec
jsPDF	7,750 /sec
Chromium/Puppeteer	~18 /sec
wkhtmltopdf	~8 /sec

Platforms

Platform	Package
macOS arm64	@slothpdf/darwin-arm64
Linux x64	@slothpdf/linux-x64

Set SLOTHPDF_LIB to use a custom binary path.

Playground

Build and preview templates at slothpdf.jsoto.cloud/editor.

License

MIT