People with admin or owner permissions can set up a CODEOWNERS file in a repository.
The people you choose as code owners must have write permissions for the repository. When the code owner is a team, that team must have write permissions, even if all the individual members of the team already have write permissions directly, through organization membership, or through another team membership.
About code owners
Code owners are automatically requested for review when someone opens a pull request that modifies code that they own. Code owners are not automatically requested to review draft pull requests. For more information about draft pull requests, see "About pull requests." When you mark a draft pull request as ready for review, code owners are automatically notified. If you convert a pull request to a draft, people who are already subscribed to notifications are not automatically unsubscribed. For more information, see "Changing the stage of a pull request."
When someone with admin or owner permissions has enabled required reviews, they also can optionally require approval from a code owner before the author can merge a pull request in the repository. For more information, see "Enabling required reviews for pull requests."
CODEOWNERS file location
To use a CODEOWNERS file, create a new file called CODEOWNERS in the root, docs/, or .github/ directory of the repository, in the branch where you'd like to add the code owners.
Each CODEOWNERS file assigns the code owners for a single branch in the repository. Thus, you can assign different code owners for different branches, such as @octo-org/codeowners-team for a code base on the default branch and @octocat for a GitHub Pages site on the gh-pages branch.
For code owners to receive review requests, the CODEOWNERS file must be on the base branch of the pull request. For example, if you assign @octocat as the code owner for .js files on the gh-pages branch of your repository, @octocat will receive review requests when a pull request with changes to .js files is opened between the head branch and gh-pages.
CODEOWNERS syntax
A CODEOWNERS file uses a pattern that follows the same rules used in gitignore files. The pattern is followed by one or more GitHub usernames or team names using the standard @username or @org/team-name format. You can also refer to a user by an email address that has been added to their GitHub Enterprise account, for example user@example.com.
If any line in your CODEOWNERS file contains invalid syntax, the file will not be detected and will not be used to request reviews. Invalid syntax includes inline comments and user or team names that do not exist on GitHub Enterprise.
Example of a CODEOWNERS file
# This is a comment.
# Each line is a file pattern followed by one or more owners.
# These owners will be the default owners for everything in
# the repo. Unless a later match takes precedence,
# @global-owner1 and @global-owner2 will be requested for
# review when someone opens a pull request.
* @global-owner1 @global-owner2
# Order is important; the last matching pattern takes the most
# precedence. When someone opens a pull request that only
# modifies JS files, only @js-owner and not the global
# owner(s) will be requested for a review.
*.js @js-owner
# You can also use email addresses if you prefer. They'll be
# used to look up users just like we do for commit author
# emails.
*.go docs@example.com
# In this example, @doctocat owns any files in the build/logs
# directory at the root of the repository and any of its
# subdirectories.
/build/logs/ @doctocat
# The `docs/*` pattern will match files like
# `docs/getting-started.md` but not further nested files like
# `docs/build-app/troubleshooting.md`.
docs/* docs@example.com
# In this example, @octocat owns any file in an apps directory
# anywhere in your repository.
apps/ @octocat
# In this example, @doctocat owns any file in the `/docs`
# directory in the root of your repository.
/docs/ @doctocat