Co-Authored-By trailer

A Co-Authored-By trailer is a one-line note added to the bottom of a commit message when you save a record in a code repository. It's similar to signing off a letter with "Co-written by: so-and-so." With this line in place, anyone looking at the history later can immediately see who was involved in that piece of work.

As AI coding tools increasingly write code on people's behalf, it's become common to put the AI's name in this trailer. That way, even though a commit might look like it was written entirely by a person, the record shows that AI was actually involved in part of it. Because the trailer is just a line of text inside the commit message, it can note a contribution without needing a link or a separate file.

In articles, you'll see phrasing like "a proposal to represent attribution using only the Co-Authored-By: Claude trailer." A common point of confusion here is mistaking this trailer for the session link that Claude Code automatically inserts into every commit. The trailer has always been the line used to mark contributors in commits, while the controversial session link is a separate URL added on top of it. Developers argued that dropping the link while keeping the trailer would be enough.

When making a commit in a code repository, try adding a line like this at the end of the message:

Co-Authored-By: Name <email address>

With this in place, the record will show exactly who helped create the commit. If the work involved an AI tool, you can put the tool's name in place of a person's name to note the distinction.