Checking for bad blocks without formatting
I'll answer the "bad blocks" tack and you can ask a follow on question if you still have slowness and you have concluded that it's not simply bad blocks. (Bad blocks is almost never a slow issue - since the system can remap blocks so rapidly, that you'd need rafts and rafts of them to actually impair I/O. If you do have bad blocks, they can corrupt some of the data on the drive and a reinstall not only fixes that, it forces writes to detect more bad blocks - kind of a win/win situation).

You need no extra tools to see the health of your drive.

Open Disk Utility and select the physical drive itself (not the Macintosh HD or whatever the partition/volume is) and select info.



If you record and watch the values under S.M.A.R.T. Status and see how they change over time, you can know pretty much anything that is detectable about storage degradation or partial failure.