Pencil is a free and open-source tool for creating diagrams, wireframes, and GUI prototypes that runs as a desktop application.
The tool addresses the need for an accessible diagramming and prototyping solution by providing a visual interface for sketching user interfaces and creating mockups. It operates as a standalone application built on Electron, allowing users to work with documents locally and export their designs in various formats including PDF.
Pencil suits designers and developers who need to create wireframes and UI prototypes without licensing costs. It works well for teams building mockups collaboratively or individuals prototyping interface designs before development. The tool is particularly useful for those already working in JavaScript-based environments, since its Electron foundation makes the codebase accessible to web developers who want to extend or customize it.
The project is actively undergoing significant architectural changes. A major rewrite introduced Electron as the runtime to replace an outdated dependency and improve developer accessibility. The new version implements a zip-based file format to handle large documents more efficiently, introduces tree-structured page management to reduce memory consumption, supports embedded custom fonts within project files, and redesigns the user interface. The development effort shows sustained focus on core performance and scalability issues that affected earlier versions.
