QUICK ANSWERStart with the tool that matches your immediate input.
Open XML Pretty Printer first when its stated purpose matches the result you need now. Use XPath Tester only when it solves a separate next task.
This guide is for developers, analysts, testers, and technical writers. Start with XML Pretty Printer when your immediate task is to use the XML Pretty Printer to inspect, transform, validate, or generate developer data locally in your browser. Move to XPath Tester only when you also need to use the XPath Tester to inspect, transform, validate, or generate developer data locally in your browser.
The goal is not to run two tools automatically. It is to finish the first narrow task, inspect its result, and then decide whether XPath Tester solves a genuinely different next step.
Both tools sit in Developer & Data, but they handle different inputs or outcomes. Keeping those roles separate reduces repeated work and makes verification easier.