fastmcp/docs/python-sdk/fastmcp-server-apps.mdx
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Co-authored-by: marvin-context-protocol[bot] <225465937+marvin-context-protocol[bot]@users.noreply.github.com>
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---
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).