OpusPad is a free Chrome add-on designed for editing Markdown files with a focus on privacy and usability. This tool offers a WYSIWYG editor that allows users to review specifications and generated plans without the clutter of raw Markdown formatting. The Source Mode feature enables precise edits, ensuring that document structure remains intact. OpusPad is built to accommodate AI-assisted development, where specifications serve as essential artifacts in the workflow.

The add-on supports local file access through Chrome's native File System API, allowing users to work directly with their project repositories. Key features include auto-save functionality, external change detection for real-time updates, and a directory sidebar for easy navigation among project files. With its lightweight design, OpusPad is optimized for quick review loops, making it an excellent choice for those needing to refine architecture specs and implementation notes while maintaining complete data privacy.