diff --git a/tools/adopt-branch.py b/tools/adopt-branch.py
new file mode 100644
index 00000000..2fe9d22f
--- /dev/null
+++ b/tools/adopt-branch.py
@@ -0,0 +1,92 @@
+"""Adopt a branch from a third party"""
+import json
+import os
+import subprocess
+import typing
+
+import click
+
+URL_RE = (
+    "(?P<repo_root>https://github.com/(?P<owner>.+)/(?P<repo>.+))/tree/(?P<branch>.+)"
+)
+
+
+class PRInfo(typing.NamedTuple):
+    owner: str
+    repo: str
+    branch: str
+    repo_url: str
+    title: str
+    body: str
+    author: str
+
+
+def command(cmd):
+    print(cmd)
+    assert os.system(cmd) == 0
+
+
+def pr_to_branch(pr_number):
+    """
+    adopt-branch pr_number
+
+    pr_number is a number like "553" or whatever.
+    """
+    result = subprocess.run(
+        [
+            "gh",
+            "pr",
+            "view",
+            str(pr_number),
+            "--json",
+            "url,headRepositoryOwner,headRepository,headRefName,title,body,author",
+        ],
+        capture_output=True,
+        text=True,  # This is to ensure that the output from the subprocess is text
+    )
+
+    assert result.returncode == 0, f"gh command failed: {result.stderr}"
+
+    pr_info = json.loads(result.stdout)
+
+    owner = pr_info["headRepositoryOwner"]["login"]
+    repo = pr_info["headRepository"]["name"]
+    branch = pr_info["headRefName"]
+    print(pr_info["headRepository"])
+
+    assert all((owner, repo, branch)), (owner, repo, branch)
+
+    return PRInfo(
+        owner,
+        repo,
+        branch,
+        repo_url=f"https://github.com/{owner}/{repo}",
+        title=pr_info["title"],
+        body=pr_info["body"],
+        author=pr_info["author"]["login"],
+    )
+
+
+@click.command()
+@click.argument("pr_number", required=True)
+def adopt_branch(pr_number):
+    """
+    adopt-branch pr_number
+
+    pr_number is a number like "553" or whatever.
+    """
+    pr_info = pr_to_branch(pr_number)
+    print("Using", pr_info.repo, pr_info.branch)
+    try:
+        command(f"git remote show {pr_info.owner} 2>/dev/null")
+    except AssertionError:
+        command(f"git remote add {pr_info.owner} {pr_info.repo_url}")
+    command(f"git fetch {pr_info.owner}")
+    command(f"git checkout --track {pr_info.owner}/{pr_info.branch}")
+    command("git push origin --set-upstream")
+    title = f"{pr_info.title} -- from @{pr_info.author}"
+    body = f"Copied from #{pr_number} by @{pr_info.author}\n\n{pr_info.body}"
+    subprocess.run(["gh", "pr", "create", "--title", title, "--body", body])
+
+
+adopt_branch()