Seven Rules

1. Separate subject from body with a blank line
2. Limit the subject line to 50 characters (max. 72), include reference (unique story ID) to requirements tracker (Pivotaltracker in our case)
3. Capitalize the subject line
4. Do not end the subject line with a period
5. Use the imperative mood in the subject line
6. Wrap the body at 72 characters
7. Use the body to explain what and why vs. how

5. Use the imperative mood in the subject line (partially extracted)

If applied, this commit will your subject line here

Good:

• If applied, this commit will refactor subsystem X for readability
• If applied, this commit will update getting started documentation
• If applied, this commit will remove deprecated methods
• If applied, this commit will release version 1.0.0
• If applied, this commit will merge pull request #123 from user/branch

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Read more Show archive.org snapshot

Bad:

• If applied, this commit will fixed bug with Y
• If applied, this commit will changing behavior of X
• If applied, this commit will more fixes for broken stuff
• If applied, this commit will sweet new API methods

Note: In feature branches the commit message also helps you to squash and fixup commits with special prefixes like fixup!.