I'm gonna assume you have 2 entities in your domain model now: Tool and Account.
Now you want to create an entity in between those two: call it LikedTool or Favourite or whatever you like to name it. It will have a many to one relation ship to both Account and Tool.
Now, if someone likes a tool, you create an object of LikedTool, associate it to the account, and associate it to the tool.
If you then count the number of LikedTool objects for a given Tool, you have the number of likes.