---
title: apps
sidebarTitle: apps
---

# `fastmcp.server.apps`


MCP Apps support — extension negotiation and typed UI metadata models.

Provides constants and Pydantic models for the MCP Apps extension
(io.modelcontextprotocol/ui), enabling tools and resources to carry
UI metadata for clients that support interactive app rendering.


## Functions

### `app_config_to_meta_dict` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/apps.py#L115" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
app_config_to_meta_dict(app: AppConfig | dict[str, Any]) -> dict[str, Any]
```


Convert an AppConfig or dict to the wire-format dict for ``meta["ui"]``.


### `resolve_ui_mime_type` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/apps.py#L122" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
resolve_ui_mime_type(uri: str, explicit_mime_type: str | None) -> str | None
```


Return the appropriate MIME type for a resource URI.

For ``ui://`` scheme resources, defaults to ``UI_MIME_TYPE`` when no
explicit MIME type is provided. This ensures UI resources are correctly
identified regardless of how they're registered (via FastMCP.resource,
the standalone @resource decorator, or resource templates).

**Args:**
- `uri`: The resource URI string
- `explicit_mime_type`: The MIME type explicitly provided by the user

**Returns:**
- The resolved MIME type (explicit value, UI default, or None)


## Classes

### `ResourceCSP` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/apps.py#L18" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Content Security Policy for MCP App resources.

Declares which external origins the app is allowed to connect to or
load resources from.  Hosts use these declarations to build the
``Content-Security-Policy`` header for the sandboxed iframe.


### `ResourcePermissions` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/apps.py#L50" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Iframe sandbox permissions for MCP App resources.

Each field, when set (typically to ``{}``), requests that the host
grant the corresponding Permission Policy feature to the sandboxed
iframe.  Hosts MAY honour these; apps should use JS feature detection
as a fallback.


### `AppConfig` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/apps.py#L77" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Configuration for MCP App tools and resources.

Controls how a tool or resource participates in the MCP Apps extension.
On tools, ``resource_uri`` and ``visibility`` specify which UI resource
to render and where the tool appears.  On resources, those fields must
be left unset (the resource itself is the UI).

All fields use ``exclude_none`` serialization so only explicitly-set
values appear on the wire.  Aliases match the MCP Apps wire format
(camelCase).

