---
title: app
sidebarTitle: app
---
# `fastmcp.apps.app`
FastMCPApp — a Provider that represents a composable MCP application.
FastMCPApp binds entry-point tools (model calls these) together with backend
tools (the UI calls these via CallTool). Backend tools are tagged with
``meta["fastmcp"]["app"]`` so they can be found through the provider chain
even when transforms (namespace, visibility, etc.) have renamed or hidden
them — the server sets a context var that tells ``Provider.get_tool`` to
fall back to a direct lookup for app-visible tools.
Usage::
from fastmcp import FastMCP, FastMCPApp
app = FastMCPApp("Dashboard")
@app.ui()
def show_dashboard() -> Component:
return Column(...)
@app.tool()
def save_contact(name: str, email: str) -> str:
return name
server = FastMCP("Platform")
server.add_provider(app)
## Classes
### `FastMCPApp`
A Provider that represents an MCP application.
Binds together entry-point tools (``@app.ui``), backend tools
(``@app.tool``), and the Prefab renderer resource. Backend tools
are tagged with ``meta["fastmcp"]["app"]`` so ``Provider.get_tool``
can find them by original name even when transforms have been applied.
**Methods:**
#### `tool`
```python
tool(self, name_or_fn: F) -> F
```
#### `tool`
```python
tool(self, name_or_fn: str | None = None) -> Callable[[F], F]
```
#### `tool`
```python
tool(self, name_or_fn: str | AnyFunction | None = None) -> Any
```
Register a backend tool that the UI calls via CallTool.
Backend tools default to ``visibility=["app"]``. Pass ``model=True``
to also expose the tool to the model (``visibility=["app", "model"]``).
Supports multiple calling patterns::
@app.tool
def save(name: str): ...
@app.tool()
def save(name: str): ...
@app.tool("custom_name")
def save(name: str): ...
#### `ui`
```python
ui(self, name_or_fn: F) -> F
```
#### `ui`
```python
ui(self, name_or_fn: str | None = None) -> Callable[[F], F]
```
#### `ui`
```python
ui(self, name_or_fn: str | AnyFunction | None = None) -> Any
```
Register a UI entry-point tool that the model calls.
Entry-point tools default to ``visibility=["model"]`` and auto-wire
the Prefab renderer resource and CSP. They are tagged with the app
name so structured content includes ``_meta.fastmcp.app``.
Supports multiple calling patterns::
@app.ui
def dashboard() -> Component: ...
@app.ui()
def dashboard() -> Component: ...
@app.ui("my_dashboard")
def dashboard() -> Component: ...
#### `add_tool`
```python
add_tool(self, tool: Tool | Callable[..., Any]) -> Tool
```
Add a tool to this app programmatically.
The tool is tagged with this app's name for routing.
#### `lifespan`
```python
lifespan(self) -> AsyncIterator[None]
```
#### `run`
```python
run(self, transport: Literal['stdio', 'http', 'sse', 'streamable-http'] | None = None, **kwargs: Any) -> None
```
Create a temporary FastMCP server and run this app standalone.