A client-side add-on for Waila or Hwyla that adds information about the harvestability of what you are looking at
By default, it shows whether or not you can currently harvest the block, the required harvest level of the block, and the tool type that is effective against the block. Plus, there are many configuration options in the Waila modules configuration screen to tweak it to show exactly what you want it to.
Note: This mod is mostly intended for use with Tinkers' Construct, but the information is still applicable without it.
The idea for the mod was suggested by DraxisWuf.
For similar functionality on Fabric, see the Can I Mine This Block? mod
Requirements
Screenshots
While holding an Iron Pickaxe (with default settings): 
Silk Touchability and Shearability:
Waila configuration screen: 
Minimal mode:
Misc
You are welcome to add this mod to any modpack you'd like.