OpenPencil

OpenPencil is a design tool open-sourced under the MIT license that can be connected to MCP with a single command, exposing more than 100 design tool interfaces and allowing agents to directly read and modify local design files.

OpenPencil's editor interface and automation interface run on the same engine.

The OpenPencil MCP service can be installed globally via npm install -g open-pencil-mcp.

OpenPencil's desktop client supports directly opening Figma-format files with two-way compatibility, has a size of approximately 7 MB, requires no account, and does not mandate an internet connection.

After OpenPencil is launched, MCP automatically discovers the running application with no manual configuration required.

In Claude Code, the claude mcp add command can be used to register OpenPencil, with --scope user enabling user-level registration that applies across all projects.

OpenPencil's five-step workflow is: list-documents to list documents, open-file or new-document to open or create, get-page-tree and find-nodes to locate nodes, render or set-fill and similar tools to make modifications, and save-file or export-svg for final delivery.

When multiple documents and pages are open simultaneously, document IDs and page IDs should be explicitly passed to tools rather than relying on the currently active tab, in order to ensure stable agent operation.

OpenPencil is configured by default with three layers of security: each tool can be individually toggled or grouped and switched by read-only/side-effect category, the HTTP service listens only on localhost by default with token authentication and the eval feature disabled by default, and file operations are restricted to authorized directories.

After modifying OpenPencil's security settings, the service must be restarted for the changes to take effect.