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At bare minimum, you will need: - a text editor - software to run and test your application - web browser There are many good text editors. Some like VIM. I often use notepad++. You could also use an integrated development environment which includes many more features. If you're writing a PHP application, you'll need an installation of PHP and a web server to run your application. I would use WAMP or XAMPP to get PHP and the web server installed and configured together. You should already have a web browser. Chrome, Firefox are great. Edge would be useful for testing small vendor-specific differences. There are many nice things to have and things that are required depending on your application's requirements. If your application needs to save any data, you'll probably want a database. Most but not all do. If your application is to run well on mobile devices, you should have a mobile phone or a few kinds to test with. Developer tools in most web browsers can simulate the dimensions of a smart phone but they don't replicate the physical screen size and user experience very well.
Thanks so much Josh. Self explanatory guidelines right there.