diff --git a/tests/test_write_tools.py b/tests/test_write_tools.py
new file mode 100644
index 0000000..50deaca
--- /dev/null
+++ b/tests/test_write_tools.py
@@ -0,0 +1,73 @@
+"""github_create_issue — the first built-out write tool.
+
+These exercise the tool's command construction and error handling WITHOUT touching
+GitHub: ``run_gh`` is patched in the ``ghplugin.write_tools`` namespace (where the tool
+looks it up), so we assert the exact ``gh issue create`` argv and the readable error
+strings. asyncio_mode=auto (see pyproject) runs the async tests directly.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, patch
+
+from ghplugin.write_tools import get_write_tools
+
+
+def _create_issue():
+    return {t.name: t for t in get_write_tools()}["github_create_issue"]
+
+
+def _labels_in(args: list[str]) -> list[str]:
+    """The value following each ``--label`` flag, in order."""
+    return [args[i + 1] for i, a in enumerate(args) if a == "--label"]
+
+
+async def test_returns_issue_url():
+    """On success the tool returns the new issue URL (gh's stdout, stripped)."""
+    tool = _create_issue()
+    fake = AsyncMock(return_value=(0, "https://github.com/o/n/issues/42\n", ""))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "o/n", "title": "Bug", "body": "It broke"})
+    assert out == "https://github.com/o/n/issues/42"
+    args = fake.call_args.args[0]
+    assert args[:4] == ["issue", "create", "--repo", "o/n"]
+    assert "--title" in args and args[args.index("--title") + 1] == "Bug"
+    assert "--body" in args and args[args.index("--body") + 1] == "It broke"
+
+
+async def test_no_labels_omits_label_flag():
+    """No labels → no --label flags at all."""
+    tool = _create_issue()
+    fake = AsyncMock(return_value=(0, "https://github.com/o/n/issues/1", ""))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        await tool.ainvoke({"repo": "o/n", "title": "t"})
+    assert "--label" not in fake.call_args.args[0]
+
+
+async def test_labels_split_into_separate_flags():
+    """Comma-separated labels become one --label flag each, stripped; blanks dropped."""
+    tool = _create_issue()
+    fake = AsyncMock(return_value=(0, "https://github.com/o/n/issues/7", ""))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        await tool.ainvoke({"repo": "o/n", "title": "t", "labels": "bug, enhancement ,"})
+    assert _labels_in(fake.call_args.args[0]) == ["bug", "enhancement"]
+
+
+async def test_bad_repo_short_circuits():
+    """An invalid repo returns the bad_repo error and never shells out."""
+    tool = _create_issue()
+    fake = AsyncMock()
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "not-a-repo", "title": "t"})
+    assert out.startswith("Error:")
+    assert "owner/name" in out
+    fake.assert_not_called()
+
+
+async def test_gh_failure_returns_check_gh_error():
+    """A nonzero gh exit becomes a readable Error string (via check_gh_error)."""
+    tool = _create_issue()
+    fake = AsyncMock(return_value=(1, "", "could not create issue: forbidden"))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "o/n", "title": "t"})
+    assert out == "Error (gh exit 1): could not create issue: forbidden"
diff --git a/write_tools.py b/write_tools.py
index 52e8fab..6125a06 100644
--- a/write_tools.py
+++ b/write_tools.py
@@ -22,7 +22,7 @@
 
 from langchain_core.tools import tool
 
-from .gh_cli import bad_repo
+from .gh_cli import bad_repo, check_gh_error, run_gh
 
 
 def get_write_tools() -> list:
@@ -36,11 +36,19 @@ async def github_create_issue(repo: str, title: str, body: str = "", labels: str
             body: Issue body (Markdown).
             labels: Optional comma-separated label names.
 
-        TODO(team): implement via `gh issue create`. Return the new issue URL.
+        Returns the new issue URL.
         """
         if err := bad_repo(repo):
             return err
-        return "Error: github_create_issue is not implemented yet (stub — to be built by the team)."
+        args = ["issue", "create", "--repo", repo, "--title", title, "--body", body]
+        for label in labels.split(","):
+            label = label.strip()
+            if label:
+                args += ["--label", label]
+        rc, out, serr = await run_gh(args)
+        if gh_err := check_gh_error(rc, serr):
+            return gh_err
+        return out.strip()
 
     @tool
     async def github_comment(repo: str, number: int, body: str) -> str: