doing mental analysis of the code you write goes a long way. know the impact of each change. know your language. have a correct model in your head of how softwa

doing mental analysis of the code you write goes a long way. know the impact of each change. know your language. have a correct model in your head of how software behaves at runtime, especially on a given OS/hw combination. this has the advantage of being language-agnostic and doesnt require tools. if you ALSO have tools, great. but in many cases you don't need them, at least if the right person is doing the right kind of thinking, at design/code/test time.