I maintain half a dozen PHP apps written for PHP 4-5, all of which now run on at least PHP 5.6, and a few of which I've gotten to PHP 7. Advice given by everyon

I maintain half a dozen PHP apps written for PHP 4-5, all of which now run on at least PHP 5.6, and a few of which I've gotten to PHP 7. Advice given by everyone else is excellent. PHPStorm is a must for me, one of the only pieces of software I pay for instead of using some OSS alternative. One thing on automated tools: getting a good result is decently tied in to the structure of your project in my experience. A common scenario I've seen is projects relying on requiring other files as part of their business logic (IE, parent file A includes file B that processes and renders content vs file B including file A that defines helpers and what not). This is especially common when projects use something like index.php?file=whatever for URLs. Most automated tools and IDEs will struggle with this and false-flag undefined variables, etc, because there is no hard include path. There are a lot of ways to resolve this but it depends on your project. Also, PHP 7 is much more aggressive about warnings on types and various other things. Unless you adjust your error reporting settings, you'll likely see a ton of these when you finally switch. I personally enable them on dev so I can clean them up, and keep them reporting to Rollbar on production.