Spell Check & Proofing

SuperDoc supports proofing on the layout-engine editor surface. Because SuperDoc renders DOCX content through its own document model and layout engine, browser-native spellcheck is not used. Instead, you provide a proofing provider and SuperDoc handles the UI: inline spelling markers, direct right-click replacement suggestions, and local ignore flows.

Quick start

const provider = {
  id: 'my-proofing',
  async check({ segments, maxSuggestions, signal }) {
    const response = await fetch('/api/proofing/check', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ segments, maxSuggestions }),
      signal,
    });

    if (!response.ok) {
      throw new Error(`Proofing request failed: ${response.status}`);
    }

    return response.json();
  },
};

new SuperDoc({
  selector: '#editor',
  document: 'contract.docx',
  proofing: {
    enabled: true,
    provider,
    defaultLanguage: 'en-US',
    maxSuggestions: 3,
    allowIgnoreWord: true,
  },
});

What SuperDoc handles

• Extracting proofable text from the document model
• Checking visible content first, then continuing in the background
• Rendering spelling markers on the layout-engine surface
• Showing provider replacement suggestions as direct context-menu actions
• Supporting Ignore for local suppression

What you provide

• A provider object with an id and check() function
• Any backend API, on-device dictionary engine, or proxy service you want to use
• Optional persistence for ignored words if you want them to survive reloads

Ignore is a SuperDoc-side suppression in v1. It only persists if your app stores ignored words and passes them back through proofing.ignoredWords.

SuperDoc does not bundle a proofing engine or send document content anywhere by default. Your provider decides where proofing runs.

Where proofing works

Proofing is available when the layout engine is active.

• In standard print layout, that works out of the box
• In web layout, use layoutEngineOptions.flowMode: 'semantic' so the layout engine stays active on a continuous surface

new SuperDoc({
  selector: '#editor',
  document: 'contract.docx',
  viewOptions: { layout: 'web' },
  layoutEngineOptions: { flowMode: 'semantic' },
  proofing: {
    enabled: true,
    provider,
  },
});

Current scope

• Spelling issues are rendered in the UI in v1
• Grammar and style issue kinds are accepted by the provider contract but are not rendered yet
• Proofing state is runtime UI state and is not written into the DOCX
• Proofing is not part of the Document API in v1

Provider options

SuperDoc does not include a spell-check engine. You bring your own provider.

• Typo.js - Simple local browser-based spell check. Good for lightweight demos, privacy-sensitive flows, and no-backend setups. See the Typo.js example.
• LanguageTool - API or self-hosted proofing with broader language support and a path to grammar checking later. See the LanguageTool self-hosted example.
• hunspell-asm - A stronger local/offline WebAssembly Hunspell option if you want a more serious on-device spell-check provider than pure JavaScript dictionaries.

Examples

See the working repo examples for two complete provider integrations:

• Typo.js example - Local, browser-only spell check with no backend
• LanguageTool self-hosted example - Self-hosted HTTP spell check with Docker

Next steps

• See Configuration for all options
• See Custom proofing provider to connect your own service