This set of d&d 5e thieves tools includes a pair of pliers , a set of narrow-bladed scissors, a small mirror mounted on a metal handle, a small file and also a set of lock picks. If you ask me what to add to thieves tools, then i would say Proficiency with these 5e thieves tools lets you add your proficiency bonus to any of the ability checks which you have to make either to disarm traps or open locks.
But here we have another query which we have got from the dungeons & dragons players and the query is how to become proficient with thieves tools? the answer is “The proficiency with a tool always allow you to add your proficiency bonus for any ability check which you do make by using the dnd 5e thieves tools.
Thieves tools 5e (Dungeons & Dragons)
Item Type: Tool