QUICK ANSWERStart with the tool that matches your immediate input.
Open Base64 Encoder and Decoder first when its stated purpose matches the result you need now. Use HTML Encoder and Decoder only when it solves a separate next task.
This guide is for developers, analysts, testers, and technical writers. Start with Base64 Encoder and Decoder when your immediate task is to open the original Base64 Encoder and Decoder and complete the task with a focused browser-based interface. Move to HTML Encoder and Decoder only when you also need to open the original HTML Encoder and Decoder and complete the task with a focused browser-based interface.
The goal is not to run two tools automatically. It is to finish the first narrow task, inspect its result, and then decide whether HTML Encoder and Decoder 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.