There is no dedicated default tool. The application remembers the last used tool.
The last used tool is updated each time an image is closed.
There is one exception. For recently used images, the tool that was used with that image is remembered.
This may sound confusing, so let me rephrase:
- If the image was recently opened (it is in the list of recently used files), the active tool (plus active colors, fill style and tool settings) are restored when the image is re-opened.
- If you create a new image or open an image that is not in the list of recently used files, the tool that was active when the last window with an image was closed is reactivated.