Break tab

The Break tab allows you to change a request or response when it has been caught by ZAP via a breakpoint.
It allows you to change elements that you would not normally be able to change via your browser, including:

The header
Hidden fields
Disabled fields
Fields that use javascript to filter out illegal characters

This functionality is key to effectively pen testing your application.

The 2 panels will only contain anything if ZAP has caught a request or response.
You can change anything in these 2 panels and then forward the request or response using the buttons on the Top Level Toolbar.

Pull downs allow you to select different Views for the request or response header and body.

While the Break tab is not in use its icon is a grey cross: .
When a breakpoint is hit the tab icon is changed to a red cross: .

Right click menu

Right clicking on a node will bring up a menu which will allow you to:

Find…

This will bring up the Find dialog.

Encode/Decode/Hash…

This will bring up the Encode/Decode/Hash dialog.
If you have highlighted any text then this will be automatically included in the dialog.

Copy

This will copy the selected string to the clipboard.

See also

UI Overview for an overview of the user interface
Breakpoints tab for details of how to change or delete breakpoints