These tools cover the settings that are short to write and easy to get wrong: a permission mode, a subnet, a container’s flags, an ignore file, a version range.
The chmod calculator converts between 755 and rwxr-xr-x, setuid, setgid and the sticky bit included, and reads the mode column of ls -l. The CIDR calculator gives a block’s range, netmask and usable hosts for IPv4 and IPv6, splits it into subnets and checks whether an address is inside. The Docker converter turns a docker run command into a Compose service and back. The gitignore generator combines templates and tests a path the way git check-ignore does, and the semver checker shows which versions an npm range like ^1.2.3 accepts.
The gotchas are the ones that bite in production. chmod 777 is never the fix for a permission error. Cloud subnets reserve addresses of their own, five in every AWS subnet, so a /24 holds fewer hosts there than on paper. A file git already tracks isn’t affected by a new ignore rule until you git rm --cached it. And ^0.2.3 allows only patch updates, because npm treats the leftmost nonzero digit as the breaking one.
The games teach the tools these settings live in: Vim Moves for getting around a file without the mouse, Git Quest for branches, merges and rebases checked against real git, and Shell Pipes for chaining commands.