Explain what a pull request merge branch is (#60712)

redsun82 · Copilot · jc-clark · web-flow · commit 6310125da98e · 2026-04-14T21:15:37.000Z
Co-authored-by: Copilot &lt;223556219+Copilot@users.noreply.github.com&gt;
Co-authored-by: Joe Clark &lt;31087804+jc-clark@users.noreply.github.com&gt;
diff --git a/content/actions/reference/workflows-and-actions/events-that-trigger-workflows.md b/content/actions/reference/workflows-and-actions/events-that-trigger-workflows.md
@@ -515,7 +515,16 @@ on:
 
 Runs your workflow when activity on a pull request in the workflow's repository occurs. For example, if no activity types are specified, the workflow runs when a pull request is opened or reopened or when the head branch of the pull request is updated. For activity related to pull request reviews, pull request review comments, or pull request comments, use the [`pull_request_review`](#pull_request_review), [`pull_request_review_comment`](#pull_request_review_comment), or [`issue_comment`](#issue_comment) events instead. For information about the pull request APIs, see [AUTOTITLE](/graphql/reference/objects#pullrequest) in the GraphQL API documentation or [AUTOTITLE](/rest/pulls).
 
-Note that `GITHUB_SHA` for this event is the last merge commit of the pull request merge branch. If you want to get the commit ID for the last commit to the head branch of the pull request, use `github.event.pull_request.head.sha` instead.
+Note that `GITHUB_SHA` for this event is the last merge commit of the pull request merge branch. If you want to get the commit ID for the last commit to the head branch of the pull request, use `github.event.pull_request.head.sha` instead. For more information about merge branches, see [AUTOTITLE](/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests#pull-request-refs-and-merge-branches).
+
+### How the merge branch affects your workflow
+
+For open, mergeable pull requests, workflows triggered by the `pull_request` event set `GITHUB_REF` to the merge branch. Because `actions/checkout` uses `GITHUB_REF` by default, it checks out the merge branch. Your CI tests run against the merged result, not just the head branch alone:
+
+* `GITHUB_REF` is set to `refs/pull/PULL_REQUEST_NUMBER/merge`
+* `GITHUB_SHA` is the SHA of the merge commit on the merge branch
+
+To test only the head branch commits without simulating a merge, check out the head branch using `github.event.pull_request.head.sha` in your workflow.
 
 For example, you can run a workflow when a pull request has been opened or reopened.
 
diff --git a/content/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests.md b/content/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests.md
@@ -35,6 +35,26 @@ When you create a pull request, you can choose to make it a draft pull request.
 
 {% data reusables.pull_requests.mark-ready-review %} You can convert a pull request to a draft at any time. See [AUTOTITLE](/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request).
 
+## Pull request refs and merge branches
+
+When you open a pull request, {% data variables.product.github %} creates up to two temporary, read-only Git references for it:
+
+| Ref | Description |
+| --- | --- |
+| `refs/pull/PULL_REQUEST_NUMBER/head` | Points to the latest commit on the pull request's head branch. |
+| `refs/pull/PULL_REQUEST_NUMBER/merge` | A merge branch—a simulated merge commit that represents what the repository would look like if the pull request were merged right now. This ref is only available when the pull request has no merge conflicts. |
+
+The merge branch automatically updates when the head branch or base branch changes. To fetch it locally:
+
+```shell
+git fetch origin refs/pull/PULL_REQUEST_NUMBER/merge
+git checkout FETCH_HEAD
+```
+
+Replace `PULL_REQUEST_NUMBER` with the number of your pull request.
+
+For information about how {% data variables.product.prodname_actions %} uses the merge branch, see [AUTOTITLE](/actions/reference/workflows-and-actions/events-that-trigger-workflows#how-the-merge-branch-affects-your-workflow).
+
 ## Differences between commits on compare and pull request pages
 
 The compare and pull request pages use different methods to calculate the diff for changed files:
diff --git a/data/reusables/actions/ref-description.md b/data/reusables/actions/ref-description.md
@@ -1 +1 @@
-The fully-formed ref of the branch or tag that triggered the workflow run. For workflows triggered by `push`, this is the branch or tag ref that was pushed. For workflows triggered by `pull_request` that were not merged, this is the pull request merge branch. If the pull request was merged, this is the head branch. For workflows triggered by `release`, this is the release tag created. For other triggers, this is the branch or tag ref that triggered the workflow run. This is only set if a branch or tag is available for the event type. The ref given is fully-formed, meaning that for branches the format is `refs/heads/<branch_name>`. For pull requests events except `pull_request_target` that were not merged, it is `refs/pull/<pr_number>/merge`. `pull_request_target` events have the `ref` from the base branch. For tags it is `refs/tags/<tag_name>`. For example, `refs/heads/feature-branch-1`.
+The fully-formed ref of the branch or tag that triggered the workflow run. For workflows triggered by `push`, this is the branch or tag ref that was pushed. For workflows triggered by `pull_request` that were not merged, this is the pull request merge branch. If the pull request was merged, this is the branch it was merged into. For workflows triggered by `release`, this is the release tag created. For other triggers, this is the branch or tag ref that triggered the workflow run. This is only set if a branch or tag is available for the event type. The ref given is fully-formed, meaning that for branches the format is `refs/heads/<branch_name>`. For pull request events except `pull_request_target` that were not merged, it is `refs/pull/<pr_number>/merge`. `pull_request_target` events have the `ref` from the base branch. For tags it is `refs/tags/<tag_name>`. For example, `refs/heads/feature-branch-1`. For more information about pull request merge branches, see [AUTOTITLE](/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests#pull-request-refs-and-merge-branches).

Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		-The fully-formed ref of the branch or tag that triggered the workflow run. For workflows triggered by `push`, this is the branch or tag ref that was pushed. For workflows triggered by `pull_request` that were not merged, this is the pull request merge branch. If the pull request was merged, this is the head branch. For workflows triggered by `release`, this is the release tag created. For other triggers, this is the branch or tag ref that triggered the workflow run. This is only set if a branch or tag is available for the event type. The ref given is fully-formed, meaning that for branches the format is `refs/heads/<branch_name>`. For pull requests events except `pull_request_target` that were not merged, it is `refs/pull/<pr_number>/merge`. `pull_request_target` events have the `ref` from the base branch. For tags it is `refs/tags/<tag_name>`. For example, `refs/heads/feature-branch-1`.
	`1`	+The fully-formed ref of the branch or tag that triggered the workflow run. For workflows triggered by `push`, this is the branch or tag ref that was pushed. For workflows triggered by `pull_request` that were not merged, this is the pull request merge branch. If the pull request was merged, this is the branch it was merged into. For workflows triggered by `release`, this is the release tag created. For other triggers, this is the branch or tag ref that triggered the workflow run. This is only set if a branch or tag is available for the event type. The ref given is fully-formed, meaning that for branches the format is `refs/heads/<branch_name>`. For pull request events except `pull_request_target` that were not merged, it is `refs/pull/<pr_number>/merge`. `pull_request_target` events have the `ref` from the base branch. For tags it is `refs/tags/<tag_name>`. For example, `refs/heads/feature-branch-1`. For more information about pull request merge branches, see [AUTOTITLE](/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests#pull-request-refs-and-merge-branches).