Stop advertising MCP_* env vars for MCPServer settings; drop pydantic-settings

The Settings docstring and the installation docs claimed MCPServer could be
configured through MCP_* environment variables and a .env file, but MCPServer
always passes explicit constructor arguments to Settings, and those outrank the
environment in pydantic-settings, so e.g. MCP_DEBUG=true has never taken effect.

Make Settings a plain pydantic BaseModel and remove pydantic-settings from the
runtime dependencies (it moves to the dev group, where the examples still use
it). The migration guide explains how to feed environment variables into the
constructor for anyone who wants that behaviour.

Author: maxisbey

docs/get-started/installation.md

@@ -34,7 +34,6 @@ You don't need to know any of this to use the SDK, but if you're wondering what
 * `mcp-types`: every protocol type (requests, results, content blocks) as its own package, versioned in lockstep with the SDK. Every `from mcp_types import ...` in these docs is this package.
 * [`anyio`](https://anyio.readthedocs.io/): the async runtime. The whole SDK is written against anyio, so it runs on either `asyncio` or `trio`.
 * [`pydantic`](https://docs.pydantic.dev/): what every `mcp_types` model is built on, plus all schema generation and validation.
-* [`pydantic-settings`](https://docs.pydantic.dev/latest/concepts/pydantic_settings/): server configuration via `MCP_*` environment variables and `.env` files.
 * [`httpx2`](https://pypi.org/project/httpx2/): the HTTP client behind the Streamable HTTP and SSE *client* transports, with server-sent events support built in.
 * [`starlette`](https://www.starlette.io/), [`uvicorn`](https://www.uvicorn.org/), [`sse-starlette`](https://pypi.org/project/sse-starlette/), and [`python-multipart`](https://pypi.org/project/python-multipart/): the HTTP *server* transports.
 * [`jsonschema`](https://pypi.org/project/jsonschema/): validates a tool's structured output against its declared output schema.

docs/migration.md

@@ -684,6 +684,22 @@ app = Starlette(routes=[Mount("/", app=mcp.streamable_http_app(json_response=Tru
 
 If you were mutating these via `mcp.settings` after construction (e.g., `mcp.settings.port = 9000`), pass them to `run()` / `sse_app()` / `streamable_http_app()` instead — these fields no longer exist on `Settings`. The `debug` and `log_level` parameters remain on the constructor.
 
+### `MCP_*` environment variables and `.env` files are no longer read
+
+The `Settings` docstring advertised configuration via `MCP_*` environment variables and a `.env` file (e.g. `MCP_DEBUG=true`), but constructor arguments have always taken precedence, so those environment variables never took effect. `Settings` is now a plain Pydantic model rather than a `pydantic-settings` `BaseSettings`, and `pydantic-settings` is no longer a dependency of the SDK.
+
+If you want environment-driven configuration, read the environment yourself and pass the values to the constructor:
+
+```python
+import os
+
+from mcp.server.mcpserver import MCPServer
+
+mcp = MCPServer("Demo", debug=os.environ.get("MCP_DEBUG") == "true")
+```
+
+If your own code uses `pydantic-settings`, add it to your project's dependencies directly.
+
 ### Streamable HTTP request bodies are limited to 4 MiB
 
 V2 applies a 4 MiB default limit to Streamable HTTP POST bodies and returns HTTP 413 before parsing

pyproject.toml

@@ -58,6 +58,9 @@ dev = [
     # We add mcp[cli] so `uv sync` considers the extras.
     "mcp[cli]",
     "mcp-example-stories",
+    # pydantic-settings is used only by examples (simple-auth, mcpserver/text_me);
+    # keep it reachable for pyright, which covers examples/servers.
+    "pydantic-settings>=2.5.2",
     "tomli>=2.0; python_version < '3.11'",
     "pyright>=1.1.400",
     "pytest>=8.4.0",
@@ -128,7 +131,6 @@ dependencies = [
     "starlette>=0.27; python_version < '3.14'",
     "python-multipart>=0.0.9",
     "sse-starlette>=3.0.0",
-    "pydantic-settings>=2.5.2",
     "uvicorn>=0.31.1; sys_platform != 'emscripten'",
     "jsonschema>=4.20.0",
     "pywin32>=311; sys_platform == 'win32'",

src/mcp/server/mcpserver/server.py

@@ -44,8 +44,8 @@
 from mcp_types import Resource as MCPResource
 from mcp_types import ResourceTemplate as MCPResourceTemplate
 from mcp_types import Tool as MCPTool
+from pydantic import BaseModel
 from pydantic.networks import AnyUrl
-from pydantic_settings import BaseSettings, SettingsConfigDict
 from starlette.applications import Starlette
 from starlette.middleware import Middleware
 from starlette.middleware.authentication import AuthenticationMiddleware
@@ -98,20 +98,8 @@
 _CallableT = TypeVar("_CallableT", bound=Callable[..., Any])
 
 
-class Settings(BaseSettings, Generic[LifespanResultT]):
-    """MCPServer settings.
-
-    All settings can be configured via environment variables with the prefix MCP_.
-    For example, MCP_DEBUG=true will set debug=True.
-    """
-
-    model_config = SettingsConfigDict(
-        env_prefix="MCP_",
-        env_file=".env",
-        env_nested_delimiter="__",
-        nested_model_default_partial_update=True,
-        extra="ignore",
-    )
+class Settings(BaseModel, Generic[LifespanResultT]):
+    """MCPServer settings, as passed to the `MCPServer` constructor."""
 
     # Server settings
     debug: bool