Sort by "Last modified" date on the index page itself. Recent modification dates (e.g., 2024 or 2025) indicate an active, maintained collection—a strong sign of quality.
In the digital landscape, a high-quality index transforms an ebook from a mere collection of text into a navigable map of knowledge index of ebooks high quality
If you love the concept of a high-quality index but want to support creators, use these legal indexes: Sort by "Last modified" date on the index page itself