HSK Characters are organized in 6 levels, ranging from beginner to near-fluency. They encapsulate about 2500 words which is the High school requirement for a student in China. With this benchmark, you are able to read novels, texts, and articles. However, about 3000 characters is a bit more of a realistic standard to pass the Chinese exams and be able to speak Chinese fluently.
The "Characters" page neatly splits up the characters of the six HSK levels into six sections. Each section increase in the number of unique characters.
If we visit the HSK 3 page by pressing the "HSK 3" button, you will find a grid of new characters that are found in the HSK 3 Book. If you press the top right button (i.e., sliders icon), you can select characters with only one specific tone (e.g., Tone 2).
At the very bottom of the screen, you will also notice a "Read" and "Write" button. As expected you can also test yourself on characters via a "Read" or "Write" Quiz.
Take a screenshot of a quiz with only characters with the fourth tone. It should look similar to the example (i.e., third tone only) above but with the fourth tone.