diff --git a/README.md b/README.md
index 1fc5626..f11c9cf 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,42 @@ Phase 4: ECOSYSTEM  (Batches 11+)   → Adjacent tools, community, competitive c
 | SaaS Product Evaluation | [saas-evaluation.md](templates/saas-evaluation.md) |
 | Programming Framework | [programming-framework.md](templates/programming-framework.md) |
 
+## MCP Server
+
+BIF includes a stdio MCP server that exposes the framework as tools for MCP-compatible clients.
+
+### Required environment
+
+| Variable | Required | Purpose |
+|----------|----------|---------|
+| `BIF_SESSIONS_DIR` | No | Overrides the default temp-directory session store. Use this when you want sessions persisted in a known workspace path. |
+
+If `BIF_SESSIONS_DIR` is not set, sessions are written under the operating system temp directory in `bif-sessions/`.
+
+### Startup command
+
+```bash
+python mcp_server.py
+```
+
+Example MCP client configuration:
+
+```json
+{
+  "mcpServers": {
+    "bif": {
+      "command": "python",
+      "args": ["/absolute/path/to/bif/mcp_server.py"],
+      "env": {
+        "BIF_SESSIONS_DIR": "/absolute/path/to/bif/.sessions"
+      }
+    }
+  }
+}
+```
+
+The server supports `initialize`, `tools/list`, `tools/call`, and `ping` over newline-delimited JSON-RPC on stdio.
+
 ## Proven Results
 
 | Project | Batches | Files | Time | Coverage |
diff --git a/tests/test_mcp_server.py b/tests/test_mcp_server.py
new file mode 100644
index 0000000..3efa07c
--- /dev/null
+++ b/tests/test_mcp_server.py
@@ -0,0 +1,66 @@
+"""Subprocess tests for the BIF MCP stdio server."""
+
+from __future__ import annotations
+
+import json
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).parent.parent
+SERVER = REPO_ROOT / "mcp_server.py"
+
+
+def _request(process: subprocess.Popen, payload: dict) -> dict:
+    assert process.stdin is not None
+    assert process.stdout is not None
+    process.stdin.write(json.dumps(payload) + "\n")
+    process.stdin.flush()
+    line = process.stdout.readline()
+    assert line, "MCP server did not emit a response"
+    return json.loads(line)
+
+
+def test_mcp_server_starts_and_accepts_tool_invocation(tmp_path) -> None:
+    env = {**os.environ, "BIF_SESSIONS_DIR": str(tmp_path / "sessions")}
+    process = subprocess.Popen(
+        [sys.executable, str(SERVER)],
+        stdin=subprocess.PIPE,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+        env=env,
+    )
+    try:
+        initialize = _request(
+            process,
+            {"jsonrpc": "2.0", "id": "init-1", "method": "initialize", "params": {}},
+        )
+        assert initialize["result"]["serverInfo"]["name"] == "bif"
+
+        tools = _request(
+            process,
+            {"jsonrpc": "2.0", "id": "tools-1", "method": "tools/list", "params": {}},
+        )
+        tool_names = {tool["name"] for tool in tools["result"]["tools"]}
+        assert "bif_start_session" in tool_names
+
+        call = _request(
+            process,
+            {
+                "jsonrpc": "2.0",
+                "id": "call-1",
+                "method": "tools/call",
+                "params": {
+                    "name": "bif_start_session",
+                    "arguments": {"domain": "MCP Test Domain"},
+                },
+            },
+        )
+        content = json.loads(call["result"]["content"][0]["text"])
+        assert content["domain"] == "MCP Test Domain"
+        assert (tmp_path / "sessions" / f"{content['session_id']}.json").exists()
+    finally:
+        process.terminate()
+        process.wait(timeout=5)