List comparer is an easy and convenient API to compare two lists for finding out common, duplicate or unique entries.

This list comparison tool will perform SET Operations over lists of words, numbers etc with formatted results
Operations including: Set Intersections (AND), Set Unions (OR) and Set Differences
Cut and Paste your lists into textbox A & B, then click Compare Lists to work out the differences between the two lists
There are other functionalities that you can perform over the results of the comparison including:

Case insensitive comparisons
Remove extraneous spaces from your input and output
Remove leading zeros from your data
The output can also be sorted with a number of formatting options including HTML, Case Capitalisations, and numbered lines

You can move the results between box A & B with the Switch function - this allows the output list to become the input list.
The layout can be changed also for mobile or limited spaced screens
There are many use-cases for the tool from Finance, Engineering and Computing to any data reconciliation tasks.
It was initially built to help with the repetitive tasks of reconciling IDs and codes in my own job