We've seen a few different ways to add Slack-style emoji search to your Mac, but Rocket's probably the simplest way to do it.
Unlike other tools we've seen, Rocket's a regular app and integrates really well into macOS. Once it's set up, just type a colon, type the name of an emoji, then tap the Return key when you have the emoji you want. If you use the colon a lot and don't want the search popping up every time you use it, you can customise the key or block Rocket from working in certain apps. It's a lot more convenient than tapping Control+Command+Space and the search works much better to boot.