diff --git a/code_review_graph/cli.py b/code_review_graph/cli.py
index 70b0b7c..dc51dd3 100644
--- a/code_review_graph/cli.py
+++ b/code_review_graph/cli.py
@@ -7,7 +7,7 @@
     code-review-graph update [--base BASE]
     code-review-graph watch
     code-review-graph status
-    code-review-graph serve
+    code-review-graph serve [--http] [--host ADDR] [--port PORT]
     code-review-graph visualize
     code-review-graph wiki
     code-review-graph detect-changes [--base BASE] [--brief]
@@ -92,7 +92,7 @@ def _print_banner() -> None:
     {g}repos{r}       List registered repositories
     {g}postprocess{r} Run post-processing {d}(flows, communities, FTS){r}
     {g}eval{r}        Run evaluation benchmarks
-    {g}serve{r}       Start MCP server
+    {g}serve{r}       Start MCP server {d}(stdio, or {g}--http{r} on localhost:5555){r}
 
   {d}Run{r} {b}code-review-graph <command> --help{r} {d}for details{r}
 """)
@@ -449,8 +449,29 @@ def main() -> None:
     detect_cmd.add_argument("--repo", default=None, help="Repository root (auto-detected)")
 
     # serve
-    serve_cmd = sub.add_parser("serve", help="Start MCP server (stdio transport)")
+    serve_cmd = sub.add_parser(
+        "serve",
+        help="Start MCP server (stdio by default, or HTTP on localhost with --http)",
+    )
     serve_cmd.add_argument("--repo", default=None, help="Repository root (auto-detected)")
+    serve_cmd.add_argument(
+        "--http",
+        action="store_true",
+        help="Listen for MCP over Streamable HTTP on localhost (default port 5555)",
+    )
+    serve_cmd.add_argument(
+        "--host",
+        default=None,
+        metavar="ADDR",
+        help="Bind address for --http (default: 127.0.0.1)",
+    )
+    serve_cmd.add_argument(
+        "--port",
+        type=int,
+        default=None,
+        metavar="PORT",
+        help="Port for --http (default: 5555)",
+    )
 
     args = ap.parse_args()
 
@@ -464,7 +485,22 @@ def main() -> None:
 
     if args.command == "serve":
         from .main import main as serve_main
-        serve_main(repo_root=args.repo)
+
+        if args.port is not None and not args.http:
+            serve_cmd.error("--port requires --http")
+        if args.host is not None and not args.http:
+            serve_cmd.error("--host requires --http")
+        if args.http:
+            host = args.host if args.host is not None else "127.0.0.1"
+            port = args.port if args.port is not None else 5555
+            serve_main(
+                repo_root=args.repo,
+                transport="streamable-http",
+                host=host,
+                port=port,
+            )
+        else:
+            serve_main(repo_root=args.repo)
         return
 
     if args.command == "eval":
diff --git a/code_review_graph/main.py b/code_review_graph/main.py
index a36f68a..00ad74b 100644
--- a/code_review_graph/main.py
+++ b/code_review_graph/main.py
@@ -1,7 +1,9 @@
 """MCP server entry point for Code Review Graph.
 
 Run as: code-review-graph serve
-Communicates via stdio (standard MCP transport).
+Communicates via stdio (standard MCP transport), or use
+``code-review-graph serve --http`` for Streamable HTTP on localhost (port 5555
+by default).
 """
 
 from __future__ import annotations
@@ -41,6 +43,7 @@
     get_suggested_questions_func,
     get_surprising_connections_func,
     get_wiki_page_func,
+    traverse_graph_func,
     list_communities_func,
     list_flows,
     list_graph_stats,
@@ -49,7 +52,6 @@
     refactor_func,
     run_postprocess,
     semantic_search_nodes,
-    traverse_graph_func,
 )
 
 # NOTE: Thread-safe for stdio MCP (single-threaded). If adding HTTP/SSE
@@ -888,8 +890,14 @@ def pre_merge_check(base: str = "HEAD~1") -> list[dict]:
     return pre_merge_check_prompt(base=base)
 
 
-def main(repo_root: str | None = None) -> None:
-    """Run the MCP server via stdio.
+def main(
+    repo_root: str | None = None,
+    *,
+    transport: str = "stdio",
+    host: str | None = None,
+    port: int | None = None,
+) -> None:
+    """Run the MCP server (stdio or HTTP).
 
     On Windows, Python 3.8+ defaults to ``ProactorEventLoop``, which
     interacts poorly with ``concurrent.futures.ProcessPoolExecutor``
@@ -898,13 +906,26 @@ def main(repo_root: str | None = None) -> None:
     ``embed_graph_tool``. Switching to ``WindowsSelectorEventLoopPolicy``
     before fastmcp starts its loop avoids the deadlock.
     See: #46, #136
+
+    Args:
+        repo_root: Optional default repository root for tools.
+        transport: ``"stdio"`` (default) or ``"streamable-http"`` for local HTTP.
+        host: Bind address when using HTTP (required for HTTP; set by CLI).
+        port: Port when using HTTP (required for HTTP; set by CLI).
     """
     global _default_repo_root
     _default_repo_root = repo_root
     if sys.platform == "win32":
         import asyncio
         asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
-    mcp.run(transport="stdio")
+    if transport == "stdio":
+        mcp.run(transport="stdio")
+    elif transport == "streamable-http":
+        if host is None or port is None:
+            raise ValueError("streamable-http transport requires host and port")
+        mcp.run(transport="streamable-http", host=host, port=port)
+    else:
+        raise ValueError(f"unsupported transport: {transport!r}")
 
 
 if __name__ == "__main__":
diff --git a/tests/test_main.py b/tests/test_main.py
index 07ee716..4230599 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -48,6 +48,47 @@ def test_client_arg_used_when_no_flag(self):
         assert crg_main._resolve_repo_root("/explicit") == "/explicit"
 
 
+class TestServeMainTransport:
+    """``main()`` wires FastMCP to stdio or Streamable HTTP."""
+
+    def test_stdio_calls_mcp_run_stdio(self, monkeypatch):
+        calls: list[dict] = []
+
+        def fake_run(**kwargs):
+            calls.append(kwargs)
+
+        monkeypatch.setattr(crg_main.mcp, "run", fake_run)
+        crg_main.main(repo_root=None)
+        assert calls == [{"transport": "stdio"}]
+
+    def test_http_calls_mcp_run_with_host_port(self, monkeypatch):
+        calls: list[dict] = []
+
+        def fake_run(**kwargs):
+            calls.append(kwargs)
+
+        monkeypatch.setattr(crg_main.mcp, "run", fake_run)
+        crg_main.main(
+            repo_root="/tmp/r",
+            transport="streamable-http",
+            host="127.0.0.1",
+            port=5555,
+        )
+        assert calls == [
+            {
+                "transport": "streamable-http",
+                "host": "127.0.0.1",
+                "port": 5555,
+            }
+        ]
+
+    def test_streamable_http_without_host_port_raises(self):
+        with pytest.raises(ValueError, match="requires host and port"):
+            crg_main.main(transport="streamable-http", host=None, port=5555)
+        with pytest.raises(ValueError, match="requires host and port"):
+            crg_main.main(transport="streamable-http", host="127.0.0.1", port=None)
+
+
 class TestLongRunningToolsAreAsync:
     """Long-running MCP tools must be registered as coroutines so the
     asyncio event loop stays responsive while the work runs in a