This is a quick blog post because I recently had to troubleshoot using this tool and I thought it would be a perfect thing to blog about. I use this tool quite a bit (mostly because I'm not all that great at base 8 math). Even if I was great at it, this would be a great tool just for saving time. https://cidr.xyz helps you visualize CIDRs.
For example, this shows mask /28 for 10.88.135.144 CIDR
You can see which bits are on/off and why the resulting CIDR range.
Some common masks are /24
/16
and /8