kagen

kagen · 紙源

紙源 · かげん - paper source. PDF generation companion to Kami.

Kami designs, Kagen ships. Converts Kami HTML templates to production-grade PDF using Chromium (Playwright), bypassing WeasyPrint's Windows limitations.

Why Kagen

Based on benchmarks (pdf4.dev 2026), engineering discussions (HN, Stack Overflow, BrowserStack), and production experience from DocRaptor, customjs.space, and print-css.rocks.

Prerequisites

• Node.js 20+
• Playwright (npx playwright auto-installs on first use)
• Chromium browser installed (npx playwright install chromium)
• Kami HTML templates (any valid HTML with print CSS)

Quick start

npx playwright pdf "file:///path/to/doc.html" "output.pdf"

Or from Node.js:

const { chromium } = require('playwright');
const browser = await chromium.launch();
const page = await browser.newPage();
await page.goto('file:///path/to/doc.html', { waitUntil: 'networkidle' });
await page.pdf({
  path: 'output.pdf',
  format: 'A4',
  printBackground: true,
  margin: { top: '0', bottom: '0', left: '0', right: '0' }
});
await browser.close();

Production settings (from professional research)

Page options

await page.pdf({
  path: 'output.pdf',
  format: 'A4',              // or 'Letter', 'A3'
  printBackground: true,     // always true — renders parchment bg
  margin: { top: '0', bottom: '0', left: '0', right: '0' },
  // For screen media (not print):
  // await page.emulateMedia({ media: 'screen' });
});

Critical CSS rules for reliable PDF output

/* Always include in your HTML template header */

@page {
  size: A4;
  margin: 24mm 26mm 26mm 26mm;
  background: #f5f4ed;
  widows: 4;
  orphans: 4;
}

/* Force background colors in Chromium */
* {
  -webkit-print-color-adjust: exact;
  print-color-adjust: exact;
}

/* Avoid orphan text lines — high widows/orphans prevents single-line splits */
body { widows: 4; orphans: 4; }
p    { widows: 3; orphans: 3; }
li   { widows: 2; orphans: 2; }

/* Page break control — only on chapters with heavy content */
.chapter { }
.chapter.break { break-before: page; }

/* Never let a heading sit alone at page bottom */
h1, h2, h3, h4 { break-after: avoid; }

/* Keep these blocks intact — never split across pages */
table, pre, figure, .callout, .card,
blockquote, .finding-header, .takeaway {
  break-inside: avoid;
}

/* Avoid code blocks getting orphaned from their preceding paragraph */
pre {
  margin-top: 6pt;
  page-break-before: avoid;
}

/* Tables should not break rows across pages */
table tr {
  break-inside: avoid;
}