Debugging tools in After Effects? Not if are seasoned in the way of scripting or writing complex and abstracting expressions, then no… AE’s tools for debugging expressions practically don’t exist. Felt Tips posts a great tutorial showing how you can create your own tools using the source text property of a text layer to find problem areas of After Effects Expressions.
Expressions in After Effects are a massively useful, but without any specific tools for the job, debugging them can be rather trickyFelt Tips - AEtuts.com
This technique uses the source text property of a Text Layer in After Effects, as it is more forgiving than other properties such as position or rotation. It is because the Source Text property can accept a wider range of input, by accepting a string, it can be used cleverly for the purposes of debugging After Effects Expressions.
Felt Tips sections the tutorial in two parts, looking first at some of the things that are possible by using a debugging layer in After Effects, writing a little function that can show the methods and properties of an object. The second part consists of a practical example, where the expression will have some errors in it, which shows how the debugger can work pragmatically.
Felt Tips give a great explanation of what expressions are doing, with a look under the hood of the After Effects Expressions engine. Check out the tutorial for Techniques for Debugging After Effects Expressions here.
Further Reading for Debugging After Effects Expressions
Chris and Trish Meyer had a great series which spoke at length on the topic of After Effects Expressions. Deeper Modes of Expressions part 12 covered everything you ever wanted to know about Expressions and Text in AE, and using a text layer for debugging expressions. Chris demonstrated ways to use After Effects expressions to manipulate text, showing how to display parameter values for creating graphical elements as well as using it for a diagnostic look at expressions.