Web小説縦読み is a free Chrome add-on developed by kinosita that enables vertical reading of multiple novel posting sites. With this add-on, users can easily read novels in a vertical format, similar to traditional Japanese books, while still being able to scroll up and down like a regular webpage.

The add-on supports various novel posting sites, including 小説家になろう, アルファポリス, 青空文庫, ハーメルン, MAGNET MACROLINK, and 暁. It provides an option to toggle the vertical reading layout on or off for each supported site.

It is worth noting that Web小説縦読み does not support vertical reading for sites like カクヨム and pixiv, as they already have built-in vertical reading functionality.

Overall, Web小説縦読み is a useful add-on for fans of Japanese novels who prefer the traditional vertical reading format. With its support for multiple novel posting sites and customizable layout options, it offers a convenient way to enjoy reading novels online.