If you've played CS:GO, you might know that there's a "crouch mode choosing" option. Well, today I'm here to show you how to have both "Crouching", and "Toggling Crouching" with any key, for Team Fortress 2. If you know how to use the developer console, or if you even know how to open it, this is going to be pretty much easy. If you don't know how to open it, then please take a look at the "How To Open Developer Console" section down below, before proceeding to the next section.

This is the main part of the whole guide, even if it's very short, it shows you how to toggle it, fully detailed. It is done through the developer's console, and you can do it with binding.
The command we'll use is "toggle_duck". In-game, this should look like this:
You should use the "bind" command. So, here is how the bind key works:
bind [yourkeyhere] "toggle_duck"
So, in-game it should be something like this:

To bind it, you must type bind [yourkeyhere] "toggle_duck". For example, to bind it to ALT, you must type in;
bind ALT "toggle_duck".
The "s are not necessary; but it's a two-word command, you need to put the "s. The "s are for the console to understand it as a single phrase, if it's a single word, then you don't need it. For example, typing bind [key] sv_cheats 1 will give you this message:
bind <key> [command] : attach a command to a key
If it is;
bind [key] "sv_cheats 1",
The console will understand it as a single command line to execute. Anyway, here's a screenshot of how it's in-game:

After you binded it to a key, just press that key to see yourself toggling crouch:)

This part is the easiest and a kinda un-necessary part. But if you want to learn how, keep reading.
Open your options, go to the "Keyboard" tab, and click "Advanced...". There'll be an option, called
"Enable Developer Console". Enable it, and you should be able to open it. If you can't open the console with the key it's supposed to open, go to TF2's launch options, and write "-console". The console should start automatically when TF2 opens up. That's it! :3 You did it!