feat(git): add prompts (git-commit-message, git-summarize-changes)

src/git/README.md

@@ -96,6 +96,23 @@ Please note that mcp-server-git is currently in early development. The functiona
      - `not_contains` (string, optional): The commit sha that branch should NOT contain. Do not pass anything to this param if no commit sha is specified
    - Returns: List of branches
 
+### Prompts
+
+In addition to tools, the server exposes prompts that assemble a ready-to-send message from real repository data:
+
+1. `git-commit-message`
+   - Generates a [Conventional Commits](https://www.conventionalcommits.org/) message for the currently staged changes
+   - Arguments:
+     - `repo_path` (string, required): Path to Git repository
+   - Returns: A user message embedding the staged diff, with instructions to draft the commit message
+
+2. `git-summarize-changes`
+   - Summarizes repository changes in plain language
+   - Arguments:
+     - `repo_path` (string, required): Path to Git repository
+     - `target` (string, optional): Branch or commit to diff against (defaults to unstaged working-tree changes)
+   - Returns: A user message embedding the diff, with instructions to summarize it
+
 ## Installation
 
 ### Using uv (recommended)

src/git/src/mcp_server_git/server.py

@@ -6,6 +6,10 @@
 from mcp.server.stdio import stdio_server
 from mcp.types import (
     ClientCapabilities,
+    GetPromptResult,
+    Prompt,
+    PromptArgument,
+    PromptMessage,
     TextContent,
     Tool,
     ListRootsResult,
@@ -108,6 +112,10 @@ class GitTools(str, Enum):
 
     BRANCH = "git_branch"
 
+class GitPrompts(str, Enum):
+    COMMIT_MESSAGE = "git-commit-message"
+    SUMMARIZE_CHANGES = "git-summarize-changes"
+
 def git_status(repo: git.Repo) -> str:
     return repo.git.status()
 
@@ -290,6 +298,38 @@ def git_branch(repo: git.Repo, branch_type: str, contains: str | None = None, no
     return branch_info
 
 
+def build_commit_message_prompt(repo: git.Repo) -> str:
+    diff = git_diff_staged(repo)
+    if not diff.strip():
+        return (
+            "There are no staged changes in this repository. Ask the user to stage "
+            "changes with `git add` before requesting a commit message."
+        )
+    return (
+        "Write a commit message for the following staged changes, following the "
+        "Conventional Commits specification (e.g. `feat:`, `fix:`, `docs:`, `refactor:`). "
+        "Use an imperative subject line under 72 characters, and add a short body only if it "
+        "adds useful context.\n\n"
+        f"Staged diff:\n```diff\n{diff}\n```"
+    )
+
+
+def build_summarize_changes_prompt(repo: git.Repo, target: str | None = None) -> str:
+    if target:
+        diff = git_diff(repo, target)
+        scope = f"compared to `{target}`"
+    else:
+        diff = git_diff_unstaged(repo)
+        scope = "in the working tree (unstaged)"
+    if not diff.strip():
+        return f"There are no changes {scope} to summarize."
+    return (
+        f"Summarize the following changes {scope} in plain language for a reviewer. Group "
+        "related changes and explain the intent behind them, not just the modified lines.\n\n"
+        f"Diff:\n```diff\n{diff}\n```"
+    )
+
+
 async def serve(repository: Path | None) -> None:
     logger = logging.getLogger(__name__)
 
@@ -582,6 +622,68 @@ async def call_tool(name: str, arguments: dict) -> list[TextContent]:
             case _:
                 raise ValueError(f"Unknown tool: {name}")
 
+    @server.list_prompts()
+    async def list_prompts() -> list[Prompt]:
+        return [
+            Prompt(
+                name=GitPrompts.COMMIT_MESSAGE,
+                description="Generate a Conventional Commits message for the currently staged changes",
+                arguments=[
+                    PromptArgument(
+                        name="repo_path",
+                        description="Path to the git repository",
+                        required=True,
+                    ),
+                ],
+            ),
+            Prompt(
+                name=GitPrompts.SUMMARIZE_CHANGES,
+                description="Summarize repository changes in plain language (working tree, or compared to a target ref)",
+                arguments=[
+                    PromptArgument(
+                        name="repo_path",
+                        description="Path to the git repository",
+                        required=True,
+                    ),
+                    PromptArgument(
+                        name="target",
+                        description="Optional branch or commit to diff against (defaults to unstaged working-tree changes)",
+                        required=False,
+                    ),
+                ],
+            ),
+        ]
+
+    @server.get_prompt()
+    async def get_prompt(name: str, arguments: dict[str, str] | None) -> GetPromptResult:
+        arguments = arguments or {}
+        if "repo_path" not in arguments:
+            raise ValueError("Missing required argument: repo_path")
+
+        repo_path = Path(arguments["repo_path"])
+        validate_repo_path(repo_path, repository)
+        repo = git.Repo(repo_path)
+
+        match name:
+            case GitPrompts.COMMIT_MESSAGE:
+                text = build_commit_message_prompt(repo)
+                description = "Draft a commit message for the staged changes"
+            case GitPrompts.SUMMARIZE_CHANGES:
+                text = build_summarize_changes_prompt(repo, arguments.get("target"))
+                description = "Summarize the repository changes"
+            case _:
+                raise ValueError(f"Unknown prompt: {name}")
+
+        return GetPromptResult(
+            description=description,
+            messages=[
+                PromptMessage(
+                    role="user",
+                    content=TextContent(type="text", text=text),
+                )
+            ],
+        )
+
     options = server.create_initialization_options()
     async with stdio_server() as (read_stream, write_stream):
         await server.run(read_stream, write_stream, options, raise_exceptions=True)

src/git/tests/test_server.py

@@ -16,6 +16,8 @@
     git_create_branch,
     git_show,
     validate_repo_path,
+    build_commit_message_prompt,
+    build_summarize_changes_prompt,
 )
 import shutil
 
@@ -482,3 +484,59 @@ def test_git_branch_rejects_contains_flag_injection(test_repository):
 
     with pytest.raises(BadName):
         git_branch(test_repository, "local", not_contains="--exec=evil")
+
+
+# Tests for prompts (git-commit-message, git-summarize-changes)
+
+def test_build_commit_message_prompt_includes_staged_diff(test_repository):
+    file_path = Path(test_repository.working_dir) / "feature.txt"
+    file_path.write_text("hello prompt world")
+    test_repository.index.add(["feature.txt"])
+
+    prompt = build_commit_message_prompt(test_repository)
+
+    assert "Conventional Commits" in prompt
+    assert "feature.txt" in prompt
+    assert "hello prompt world" in prompt  # the staged diff is embedded in the prompt
+
+
+def test_build_commit_message_prompt_no_staged_changes(test_repository):
+    prompt = build_commit_message_prompt(test_repository)
+
+    assert "no staged changes" in prompt.lower()
+
+
+def test_build_summarize_changes_prompt_unstaged(test_repository):
+    file_path = Path(test_repository.working_dir) / "test.txt"
+    file_path.write_text("rewritten content")
+
+    prompt = build_summarize_changes_prompt(test_repository)
+
+    assert "working tree" in prompt
+    assert "rewritten content" in prompt
+
+
+def test_build_summarize_changes_prompt_with_target(test_repository):
+    default_branch = test_repository.active_branch.name
+    test_repository.git.checkout("-b", "summary-branch")
+    file_path = Path(test_repository.working_dir) / "test.txt"
+    file_path.write_text("branch content")
+    test_repository.index.add(["test.txt"])
+    test_repository.index.commit("branch commit")
+
+    prompt = build_summarize_changes_prompt(test_repository, default_branch)
+
+    assert default_branch in prompt
+    assert "branch content" in prompt
+
+
+def test_build_summarize_changes_prompt_no_changes(test_repository):
+    prompt = build_summarize_changes_prompt(test_repository)
+
+    assert "no changes" in prompt.lower()
+
+
+def test_build_summarize_changes_prompt_rejects_flag_injection(test_repository):
+    """The summarize prompt reuses git_diff, so it inherits the '-' guard."""
+    with pytest.raises(BadName):
+        build_summarize_changes_prompt(test_repository, "--output=/tmp/evil")