Allow to check out branches

The git server currently lacks branch switching capabilities, limiting both
LLMs and developers. This adds branch checkout so LLMs can
help developers add new functionality in a new feature branch.

Author: mikegehard

src/git/pyproject.toml

@@ -30,4 +30,10 @@ requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [tool.uv]
-dev-dependencies = ["pyright>=1.1.389", "ruff>=0.7.3"]
+dev-dependencies = ["pyright>=1.1.389", "ruff>=0.7.3", "pytest>=8.0.0"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = "test_*.py"
+python_classes = "Test*"
+python_functions = "test_*"

src/git/src/mcp_server_git/server.py

@@ -44,6 +44,10 @@ class GitCreateBranch(BaseModel):
     branch_name: str
     base_branch: str | None = None
 
+class GitCheckout(BaseModel):
+    repo_path: str
+    branch_name: str
+
 class GitTools(str, Enum):
     STATUS = "git_status"
     DIFF_UNSTAGED = "git_diff_unstaged"
@@ -53,6 +57,7 @@ class GitTools(str, Enum):
     RESET = "git_reset"
     LOG = "git_log"
     CREATE_BRANCH = "git_create_branch"
+    CHECKOUT = "git_checkout"
 
 def git_status(repo: git.Repo) -> str:
     return repo.git.status()
@@ -96,6 +101,10 @@ def git_create_branch(repo: git.Repo, branch_name: str, base_branch: str | None
     repo.create_head(branch_name, base)
     return f"Created branch '{branch_name}' from '{base.name}'"
 
+def git_checkout(repo: git.Repo, branch_name: str) -> str:
+    repo.git.checkout(branch_name)
+    return f"Switched to branch '{branch_name}'"
+
 async def serve(repository: Path | None) -> None:
     logger = logging.getLogger(__name__)
 
@@ -152,6 +161,11 @@ async def list_tools() -> list[Tool]:
                 description="Creates a new branch from an optional base branch",
                 inputSchema=GitCreateBranch.schema(),
             ),
+            Tool(
+                name=GitTools.CHECKOUT,
+                description="Switches branches",
+                inputSchema=GitCheckout.schema(),
+            ),
         ]
 
     async def list_repos() -> Sequence[str]:
@@ -249,6 +263,13 @@ async def call_tool(name: str, arguments: dict) -> list[TextContent]:
                     text=result
                 )]
 
+            case GitTools.CHECKOUT:
+                result = git_checkout(repo, arguments["branch_name"])
+                return [TextContent(
+                    type="text",
+                    text=result
+                )]
+
             case _:
                 raise ValueError(f"Unknown tool: {name}")
 

src/git/tests/test_server.py

@@ -0,0 +1,24 @@
+import pytest
+from pathlib import Path
+import git
+from mcp_server_git.server import git_checkout
+
+def test_git_checkout_existing_branch(tmp_path: Path):
+    # Setup test repo
+    repo = git.Repo.init(tmp_path)
+    Path(tmp_path / "test.txt").write_text("test")
+    repo.index.add(["test.txt"])
+    repo.index.commit("initial commit")
+
+    # Create and test branch
+    repo.git.branch("test-branch")
+    result = git_checkout(repo, "test-branch")
+
+    assert "Switched to branch 'test-branch'" in result
+    assert repo.active_branch.name == "test-branch"
+
+def test_git_checkout_nonexistent_branch(tmp_path: Path):
+    repo = git.Repo.init(tmp_path)
+
+    with pytest.raises(git.GitCommandError):
+        git_checkout(repo, "nonexistent-branch")