Insphpect analyses your code for design patterns which are known bad practices and introduce negative traits such as tight coupling and global state.

How is it different from Scruitnizer/phpmd/etc?

Insphpect looks for software traits that lead to poor flexibility. The aforementioned tools mostly use size based metrics like cyclomatic complexity (the numnber of if statements, loops and functions) to grade your classes.

For example, in Scruitnizer A class with 34 complexity gets an A and a class with 35 complexity gets a B. This 35 cut-off is arbitrary and only indicative of problems in your code.

Although it's a bit more complex than that, such tools grade your code on simple tallies of the weight of your code (number of methods, cyclomatic complexity number of coupled classes, etc).

Instead of using statistical metrics which focus on code weight, insphpect looks for specific design patterns which are known to made code difficult to maintain and extend. For example, singletons and global variables. It uses these, rather than the simply weighing the size of your classes to grade your code.