Edmundmiller Opencode Canvas Document

Document Canvas

Display markdown documents with optional text selection and diff highlighting.

Example Prompts

Try asking:

• "Draft an email to the marketing team about the Q1 product launch"
• "Help me edit this blog post - show it so I can highlight the parts to revise"
• "Write a project proposal and let me review it"
• "Show me the README so I can select sections to update"
• "Compose a response to this customer complaint"

OpenCode Tools

High-Level (Recommended)

Display a document (read-only):

Use canvas_display_document with:
  content: "# My Document\n\nMarkdown content here."
  title: "Document Title"
  diffs: [{ startOffset: 10, endOffset: 20, type: "added" }]  // optional

Edit/select from a document:

Use canvas_edit_document with:
  content: "# My Document\n\nSelect some text here."
  title: "Edit Mode"

Low-Level (Full Control)

Use canvas_spawn with:
  kind: "document"
  scenario: "edit" or "display" or "email-preview"
  config: { content: "...", title: "..." }

Scenarios

display (default)

Read-only document view with markdown rendering. User can scroll but cannot select text.

edit

Interactive document view with text selection. User can click and drag to select text, which is returned when canvas closes.

• Renders markdown with syntax highlighting (headers, bold, italic, code, links, lists, blockquotes)
• Diff highlighting: green background for additions, red for deletions
• Click and drag to select text
• Selection returned on close

email-preview

Specialized view for email content display with email-specific formatting.

Configuration

interface DocumentConfig {
  content: string;        // Markdown content
  title?: string;         // Document title (shown in header)
  diffs?: DocumentDiff[]; // Optional diff markers for highlighting
  readOnly?: boolean;     // Disable selection (default: false for edit)
}

interface DocumentDiff {
  startOffset: number;    // Character offset in content
  endOffset: number;
  type: "added" | "removed" | "modified";
}

Markdown Rendering

Supported markdown features:

• Headers (# H1, ## H2, etc.)
• Bold (**text**)
• Italic (*text*)
• Code (`inline` and fenced blocks)
• Links ([text](url))
• Lists (- or * bullets)
• Blockquotes (>)

Selection Result

interface DocumentSelection {
  selectedText: string;   // The selected text
  startOffset: number;    // Start character offset
  endOffset: number;      // End character offset
  startLine: number;      // Line number (1-based)
  endLine: number;
  startColumn: number;    // Column in start line
  endColumn: number;
}

Controls

• Mouse click and drag: Select text (edit scenario)
• Up/Down or scroll: Navigate document
• q or Esc: Close/cancel

Active Canvas Operations

After spawning with canvas_spawn, you can:

Use canvas_get_selection to get current text selection
Use canvas_get_content to get full document content
Use canvas_update to change content/config
Use canvas_close to close the canvas

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