PlantUML Visualizer is a Chrome extension developed by WillBooster Inc. It provides a convenient way to visualize PlantUML descriptions as diagrams. With this extension, users can easily view and understand PlantUML descriptions on various web pages.

The extension supports visualization of PlantUML descriptions on GitHub. Users can view diagrams in the file viewer, including those with the `!include` directive. Additionally, diagrams in GitHub issues and pull requests can also be visualized. The extension even supports rendering of code blocks in README files or other similar documents on GitHub.

Furthermore, the extension allows users to visualize PlantUML descriptions in any .pu, .puml, .plantuml, or .wsd files. On Chrome, it even supports visualization of diagrams in GitHub raw files. However, it's important to note that the extension may not work with GitHub raw files on Firefox due to a known bug.

For local files, the extension supports visualization of diagrams, but it does not support the `!include` directive for security reasons. Users can use other software, such as the official PlantUML renderer, for rich rendering of local files.

Overall, PlantUML Visualizer is a useful Chrome extension that simplifies the visualization of PlantUML descriptions, making it easier for users to understand and work with these diagrams.