Burp Comparer is a Burp feature used for comparing differences based on the word or byte comparison. The comparison can be used in a lot of conditions. For example, let's say the user wants to compare the difference on a successful and a failed login response. Comparer would show the areas where there are byte differences. One of the other uses that we can think of is for testing SQL injection to see the difference. There are two types of comparison. To send responses to the Comparer, simply right-click on the response and Send to Comparer. For reference, have a look at the following screenshot:

For clarification, we have sent two different responses to Comparer: one of a successful login and another for an unsuccessful login. The Comparer toolbar would look as follows:

The tester can then select one response from item 1 and another response from item 2, and click on Compare by words, and Compare by bytes. The tool will do a word-to-word comparison and show the differences like deletion, modification, and addition, for example:

The comparison is shown in a color-coded scheme, as we can see in the preceding screenshot for Modified, Deleted, and Added.