Most combolists are simple .txt files containing credentials in a standard email:password or user:pass format.

A is a massive text file containing millions of stolen email addresses and passwords, often categorized by specific interests like "lifestyle and entertainment" to help cybercriminals target high-value accounts . These files are not legitimate downloads but are "Compilations of Multiple Breaches" (combolists) aggregated from various leaks and used for automated attacks. The Anatomy of a Combolist

How Attackers Use Password Combolists in Brute-Force Campaigns