Which file format is used for Docker Compose files?

Docker Compose files utilize the YAML format, which stands for "YAML Ain't Markup Language." This format is specifically designed to be both human-readable and easily writable, making it an ideal choice for defining multi-container Docker applications.

YAML's structure allows for representation of complex data types in a clean and intuitive way, using indentation to denote hierarchy, which aligns well with the needs of describing multiple services, networks, and volumes in a Docker Compose environment. This is crucial for ensuring that developers can quickly understand and modify configuration files without confusion.

In contrast to other formats listed, such as JSON, XML, or plain text, YAML's design reduces syntactical clutter. For example, JSON requires the use of braces and commas, which can complicate readability, especially for nested structures. XML can be verbose and more difficult to parse visually. Plain text is not structured enough to capture the complexities of Docker Compose files, such as dependencies among services and environment configurations.

Using YAML for Docker Compose files thus enhances clarity, provides necessary structure, and aids maintainability, which is why it is the preferred choice in the Docker ecosystem.