YML (YAML Alias)
YML is an alternative file extension for YAML files, functionally identical to .yaml. Both extensions are widely used, with .yml being more common in some ecosystems (Docker Compose, GitHub Actions) and .yaml preferred by the official YAML specification.
MIME Type
application/x-yaml
Type
Text
Compression
Lossless
Advantages
- + Shorter extension, widely recognized
- + Default in Docker Compose (docker-compose.yml)
- + Used by GitHub Actions (.github/workflows/*.yml)
Disadvantages
- − Not the officially recommended extension (.yaml is preferred)
- − Inconsistency between .yml and .yaml can confuse tooling
- − Same indentation pitfalls as .yaml
When to Use .YML
Use .yml or .yaml consistently within a project; .yml is common for Docker Compose and GitHub Actions, while .yaml is the official extension.
Technical Details
Identical to .yaml files — same YAML specification, same parser, same features. The file extension is purely cosmetic and does not affect parsing behavior.
History
The .yml extension emerged as a shorter alternative to .yaml, following the convention of three-character extensions. Many tools accept both, and the choice is largely a matter of project convention.