"Serious" crimping tools cost a lot, often outrageously expensive. I still ended up buying one at "only" $50, and it improve both my productivity and the reliability of my connections a lot. Specifically, and foremost if you just want to buy only one, like I did initially, I highly recommend the PA-09 (the one below), which is suited for all Molex & JST crimps I use as a DIY/semi pro.

I liked this japanese "Engineer" brand so much that I then happily bought the larger PA-20 (I do not use it often), and a neat wire stripping tool for small diameters (which I use all the time, even though I have to admit that cheap ones do the job, there).

In any case, I will not crimp ever again with flat nose pliers.

Here is a video of the thing in action: https://www.youtube.com/watch?v=xxMYjJ4Lwi0
It looks deceptively simple, but the precision of the pliers is the key here. This is real japanese stuff, not low cost chinese, and for once it really shows up even at the hobbyist level. Hey look, even Andreas Spiess says the same: https://www.youtube.com/watch?v=3Cw9YFLDZeo
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