Overview

What are Flags?

In CTFs, a flag is the proof that a participant has successfully completed a challenge. Flags are typically strings of text that participants must discover by solving puzzles, exploiting vulnerabilities, or demonstrating knowledge of specific concepts.

In CTFd, when a user submits a flag, CTFd verifies it against stored flag(s) and awards points if the submission is correct.

Flag Types

CTFd supports multiple flag types to accommodate different challenge designs and verification requirements. Each flag type offers different capabilities and options for how submissions are validated. In the following pages you can read more about each flag type available in CTFd.

Extending Flag Types

CTFd's flag system is extensible through plugins. Developers can create custom flag types to implement specialized validation logic that isn't available in the built-in types.

For information on creating custom flag type plugins, see the Flag Type Plugins page.