TonalEnergy Tuner is recommended by David Moore, so I went with it.
It is an inexpensive app you can install on your phone or iPad.
https://www.tonalenergy.com/
There is something about the lowest notes on a bass that makes it very difficult to be in tune. I regularly play around on the violin and it is easier to be in tune than our basses.
The beauty of TE Tuner is you can see clearly where and how much you are off. You can play along with a drone. It does a lot more than only telling you how in tune you are. Check out the link.
Many say they don’t get the point of playing with a tuner. It’s recommended by David Moore, who kinda knows more than most of us here. Playing with a tuner is another practice tool to be better in tune when you play with people.
Top violin soloists do this kind of practice. It’s not meant to be used as a crutch, but a tool to improve.