Question: I want to develop a very simple Extension which :

* searches the current contact\_id
* then verifies if he is recorded for a given event (event\_id as a parameter)
* then, depending on the result, echoes a message or opens an URL.

I read that, to develop an extension, I first had to :

* install Civix,
* which requires installing first git and composer
... which seems very complicated to me for such a simple program.

Is there a way to write and upload directly the code in the Extension directory, whithout all these prerequisites ?

Answer: 
git and composer aren't necessary to install civix. In the [README](https://github.com/totten/civix/blob/master/README.md) it suggests multiple ways to install civix. The first one is a simple download: <https://download.civicrm.org/civix/civix.phar>.
Yes, you could also just create a folder with the name of your extension in the extension folder of CiviCRM, and code from there. But that requires you to understand the folder and file structure required for extensions so it will actually be easier with civix. It is not a prerequisite but it helps a lot!