This editor extension allows the user to update tile sheets to eliminate the cause of gaps between tiles.

Gaps occur due to the rendering engine looking at pixels outside the edges of the tiles in the tilesheet. This tool surrounds each tile with a ring of pixels that match the pixels on the edges of the tile. The Unity tile rendering engine will then fill gaps with these pixels, thus removing the gaps.

The fix can be applied by hand, and if you are starting a new project then I recommend doing this. During tile creation it will only take a relatively small amount of time.

This video explains the issue in detail, and provides a solution:

video

However, if you do not have access to design tools or resources, you may find it difficult to make the required changes. Or if a project is mature, you could be looking at thousands of tiles to fix.

This editor panel takes the sting out of the process by automating the fix and allowing tile sheets to be updated "in place". If the original tile sheet has space for the new padding pixels, no further configuration will be required and gaps will be automatically eliminated. If the original tile sheet needs expanding to make room for the new pixels, the panel will prompt the user with the new required settings for entry into the sprite editor's slice tool.

Please be aware, this tool is only compatible with .png format tilesheets.