Fonts

Base URL for self-hosted font files — self-hosting licenses only. It relocates only the SDK's own bundled fonts, so it needs a license that includes self-hosting (today, an offline license); otherwise the first text tool the user opens is refused with FEATURE_NOT_LICENSED. Fetch each file once from the store by Kernstra.assetDigests.fonts[font.id] and serve it under its ttfPath — see Engine, binaries and fonts. The SDK verifies their bytes exactly as it verifies a download, unless you turn that off with verifyIntegrity: false.

// Self-host all fonts (self-hosting license)
fonts: {
  fontsBaseUrl: '/assets/fonts/',
}

false = airgapped mode, no font downloads: the standard-14 fonts, fonts embedded in the document, and customFonts registered with ttfBytes keep working with zero network access; loading any other font — a bundled one, or a custom font registered by URL — rejects with a descriptive error.

// Airgapped deployment — no font downloads at all
fonts: {
  download: false,
}

SHA-256 verify downloaded bundled fonts. Downloads from the store are always verified. false is only needed when self-hosting _modified_ font files under the same ids via fontsBaseUrl; exact copies of the original files pass verification.

Embed only the glyphs an edit uses. By default an edit embeds the whole font for every face it touches, so a document a customer saves today can be reopened and edited in the same faces any number of times — every glyph is still there. true embeds only the glyphs the edit wrote, which keeps exported files small (a few kilobytes per face instead of a few hundred, or several megabytes for CJK) at a price: a later edit of that document that needs a glyph outside the subset falls back to a bundled look-alike, exactly as it does for any subset font other tools produce. Turn it on when file size matters more than round-trip re-editability, for example single-pass workflows or size-capped uploads. Subsetting needs pdf-subset.bin to load (see Engine, binaries and fonts) and falls back to full fonts, with one console warning, when it does not.

Your own fonts: the same bag FontRegistry.registerCustomFont() takes. Your own fonts are never gated. customFonts (a URL you serve or bytes you hold) works under every license, and so do the fonts embedded in the documents you open. The license governs where _our_ fonts come from, not which fonts you use. A viewer's fonts are the ones customFonts names when it is created; there is no method to add one to a running viewer. FontRegistry is exported for loading fonts outside a viewer — fonts you register with one you construct yourself are not seen by any viewer.

// Register a custom font from URL
fonts: {
  customFonts: [
    {
      id: 'my-serif',
      displayName: 'My Serif',
      ttfUrl: 'https://cdn.example.com/fonts/MySerif-Regular.ttf',
      category: 'serif',
    },
  ],
}

The list both text tools' size menus offer, in points; positive numbers only, sorted. A block whose size is not in the list still shows its own size. New text starts at 18 pt, or at the listed size nearest it when 18 is not listed.