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jlowin merged 3 commits into from
Feb 11, 2026
Merged

Remove deprecated FastMCP() constructor kwargs #3148

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cd7f985
Remove deprecated FastMCP() constructor kwargs
jlowin Feb 11, 2026
29a37a8
chore: Update SDK documentation
marvin-context-protocol[bot] Feb 11, 2026
ac00017
Fix review feedback: is not None checks, docs method name
jlowin Feb 11, 2026
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56 changes: 28 additions & 28 deletions docs/development/v3-notes/v3-features.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,32 @@ async def get_emails(

Background tasks now use a distributed Redis notification queue for reliable delivery ([#2906](https://github.com/jlowin/fastmcp/pull/2906)). Elicitation switches from polling to BLPOP (single blocking call instead of ~7,200 round-trips/hour), and notification delivery retries up to 3x with TTL-based expiration.

### Breaking: Deprecated `FastMCP()` Constructor Kwargs Removed

Sixteen deprecated keyword arguments have been removed from `FastMCP.__init__`. Passing any of them now raises `TypeError` with a migration hint. Environment variables (e.g., `FASTMCP_HOST`) continue to work — only the constructor kwargs moved.

**Transport/server settings** (`host`, `port`, `log_level`, `debug`, `sse_path`, `message_path`, `streamable_http_path`, `json_response`, `stateless_http`): Pass to `run()`, `run_http_async()`, or `http_app()` as appropriate, or set via environment variables.

```python
# Before
mcp = FastMCP("server", host="0.0.0.0", port=8080)
mcp.run()

# After
mcp = FastMCP("server")
mcp.run(transport="http", host="0.0.0.0", port=8080)
```

**Duplicate handling** (`on_duplicate_tools`, `on_duplicate_resources`, `on_duplicate_prompts`): Use the unified `on_duplicate=` parameter.

**Tag filtering** (`include_tags`, `exclude_tags`): Use `server.enable(tags=..., only=True)` and `server.disable(tags=...)` after construction.

**Tool serializer** (`tool_serializer`): Return `ToolResult` from tools instead.

**Tool transformations** (`tool_transformations`): Use `server.add_transform(ToolTransform(...))` after construction.

The `_deprecated_settings` attribute and `.settings` property are also removed. `ExperimentalSettings` has been deleted (dead code).

### Breaking: `ui=` Renamed to `app=`

The MCP Apps decorator parameter has been renamed from `ui=ToolUI(...)` / `ui=ResourceUI(...)` to `app=AppConfig(...)` ([#3117](https://github.com/jlowin/fastmcp/pull/3117)). `ToolUI` and `ResourceUI` are consolidated into a single `AppConfig` class. Wire format is unchanged. See the MCP Apps section under beta2 for full details.
Expand Down Expand Up @@ -1266,35 +1292,9 @@ main.mount(subserver, prefix="api")
main.mount(subserver, namespace="api")
```

#### Tag Filtering Init Parameters

`FastMCP(include_tags=..., exclude_tags=...)` deprecated. Use `enable()`/`disable()` methods:
#### Tag Filtering, Tool Serializer, Tool Transformations Init Parameters

```python
# Deprecated
mcp = FastMCP("server", exclude_tags={"internal"})

# New
mcp = FastMCP("server")
mcp.disable(tags={"internal"})
```

#### Tool Serializer Parameter

The `tool_serializer` parameter on `FastMCP` is deprecated. Return `ToolResult` for explicit serialization control.

#### Tool Transformation Methods

`add_tool_transformation()`, `remove_tool_transformation()`, and `tool_transformations` constructor parameter are deprecated. Use `add_transform(ToolTransform({...}))` instead:

```python
# Deprecated
mcp.add_tool_transformation("name", config)

# New
from fastmcp.server.transforms import ToolTransform
mcp.add_transform(ToolTransform({"name": config}))
```
These constructor parameters have been **removed** (not just deprecated) as of rc1. See "Breaking: Deprecated `FastMCP()` Constructor Kwargs Removed" in the rc1 section above. The `add_tool_transformation()` and `remove_tool_transformation()` methods remain as deprecated shims.

---

Expand Down
32 changes: 16 additions & 16 deletions docs/python-sdk/fastmcp-mcp_config.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ infer_transport_type_from_url(url: str | AnyUrl) -> Literal['http', 'sse']
Infer the appropriate transport type from the given URL.


### `update_config_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L321" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `update_config_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L324" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
update_config_file(file_path: Path, server_name: str, server_config: CanonicalMCPServerTypes) -> None
Expand All @@ -57,7 +57,7 @@ worry about transforming server objects here.

## Classes

### `StdioMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L131" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `StdioMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L134" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


MCP server configuration for stdio transport.
Expand All @@ -67,19 +67,19 @@ This is the canonical configuration format for MCP servers using stdio transport

**Methods:**

#### `to_transport` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L164" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `to_transport` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L167" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_transport(self) -> StdioTransport
```

### `TransformingStdioMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L176" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `TransformingStdioMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L179" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


A Stdio server with tool transforms.


### `RemoteMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L180" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `RemoteMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L183" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


MCP server configuration for HTTP/SSE transport.
Expand All @@ -89,19 +89,19 @@ This is the canonical configuration format for MCP servers using remote transpor

**Methods:**

#### `to_transport` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L216" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `to_transport` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L219" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_transport(self) -> StreamableHttpTransport | SSETransport
```

### `TransformingRemoteMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L241" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `TransformingRemoteMCPServer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L244" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


A Remote server with tool transforms.


### `MCPConfig` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L252" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `MCPConfig` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L255" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


A configuration object for MCP Servers that conforms to the canonical MCP configuration format
Expand All @@ -113,7 +113,7 @@ For an MCPConfig that is strictly canonical, see the `CanonicalMCPConfig` class.

**Methods:**

#### `wrap_servers_at_root` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L266" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `wrap_servers_at_root` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L269" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
wrap_servers_at_root(cls, values: dict[str, Any]) -> dict[str, Any]
Expand All @@ -122,7 +122,7 @@ wrap_servers_at_root(cls, values: dict[str, Any]) -> dict[str, Any]
If there's no mcpServers key but there are server configs at root, wrap them.


#### `add_server` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L279" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `add_server` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L282" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
add_server(self, name: str, server: MCPServerTypes) -> None
Expand All @@ -131,7 +131,7 @@ add_server(self, name: str, server: MCPServerTypes) -> None
Add or update a server in the configuration.


#### `from_dict` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L284" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `from_dict` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L287" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
from_dict(cls, config: dict[str, Any]) -> Self
Expand All @@ -140,7 +140,7 @@ from_dict(cls, config: dict[str, Any]) -> Self
Parse MCP configuration from dictionary format.


#### `to_dict` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L288" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `to_dict` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L291" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_dict(self) -> dict[str, Any]
Expand All @@ -149,7 +149,7 @@ to_dict(self) -> dict[str, Any]
Convert MCPConfig to dictionary format, preserving all fields.


#### `write_to_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L292" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `write_to_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L295" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
write_to_file(self, file_path: Path) -> None
Expand All @@ -158,7 +158,7 @@ write_to_file(self, file_path: Path) -> None
Write configuration to JSON file.


#### `from_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L298" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `from_file` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L301" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
from_file(cls, file_path: Path) -> Self
Expand All @@ -167,7 +167,7 @@ from_file(cls, file_path: Path) -> Self
Load configuration from JSON file.


### `CanonicalMCPConfig` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L306" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
### `CanonicalMCPConfig` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L309" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Canonical MCP configuration format.
Expand All @@ -178,7 +178,7 @@ The format is designed to be client-agnostic and extensible for future use cases

**Methods:**

#### `add_server` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L316" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
#### `add_server` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/mcp_config.py#L319" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
add_server(self, name: str, server: CanonicalMCPServerTypes) -> None
Expand Down
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