LangExtract MCP Server

Instructions

Implementation Reference

• src/langextract_mcp/server.py:451-502 (handler)

  The handler function that implements the generate_visualization tool. It loads the JSONL extraction results, uses langextract.visualize to create an interactive HTML visualization highlighting entities in context, handles output path (auto or specified), and returns the generated file path.

  def generate_visualization(
      jsonl_file_path: str,
      output_html_path: str | None = None
  ) -> dict[str, str]:
      """
      Generate interactive HTML visualization from extraction results.
      
      Creates an interactive HTML file that shows extracted entities highlighted
      in their original text context. The visualization is self-contained and
      can handle thousands of entities with color coding and hover details.
      
      Args:
          jsonl_file_path: Path to the JSONL file containing extraction results
          output_html_path: Optional path for the HTML output (default: auto-generated)
          
      Returns:
          Dictionary with HTML file path and generation details
          
      Raises:
          ToolError: If visualization generation fails
      """
      try:
          # Validate input file exists
          input_path = Path(jsonl_file_path)
          if not input_path.exists():
              raise ToolError(f"Input file not found: {jsonl_file_path}")
          
          # Generate visualization using langextract
          html_content = lx.visualize(str(input_path))
          
          # Determine output path
          if output_html_path:
              output_path = Path(output_html_path)
          else:
              output_path = input_path.parent / f"{input_path.stem}_visualization.html"
          
          # Ensure output directory exists
          output_path.parent.mkdir(parents=True, exist_ok=True)
          
          # Write HTML file
          with open(output_path, 'w', encoding='utf-8') as f:
              f.write(html_content)
          
          return {
              "message": "Visualization generated successfully",
              "html_file_path": str(output_path.absolute()),
              "file_size_bytes": len(html_content.encode('utf-8'))
          }
          
      except Exception as e:
          raise ToolError(f"Failed to generate visualization: {str(e)}")

• src/langextract_mcp/server.py:450-450 (registration)

  The @mcp.tool decorator that registers the generate_visualization function as an MCP tool with FastMCP.

  @mcp.tool