ReadComicsOnline is a website for browsing and reading comic previews, bringing together thousands of issues from major publishers and independent creators. Its catalogue includes more than 5,300 issues, with titles from Marvel, DC Comics, Image Comics, Dark Horse Comics, and other publishers. Readers can explore ongoing and completed series, browse by genre or character, search for specific comics, and follow new issues added daily. Featured characters and popular series include Batman, Spider-Man, the X-Men, and the Avengers, alongside a regularly updated selection of superhero, action, adventure, science-fiction, fantasy, horror, crime, and comedy comics.

Beyond its catalogue, the site offers reading orders to help visitors decide where to begin with a character, comic trivia quizzes, news and features, and a service for requesting missing series. Comics can be browsed without registration, while an optional ad-free plan is available for $3 per month; visitors can also tip the site. ReadComicsOnline states that it does not host files itself and that its content is provided by unaffiliated third parties.