base

fastmcp.resources.base

Base classes and interfaces for FastMCP resources.

Classes

ResourceContent

Wrapper for resource content with optional MIME type and metadata.

Accepts any value for content - strings and bytes pass through directly, other types (dict, list, BaseModel, etc.) are automatically JSON-serialized.

Methods:

to_mcp_resource_contents

to_mcp_resource_contents(self, uri: AnyUrl | str) -> mcp.types.TextResourceContents | mcp.types.BlobResourceContents

Convert to MCP resource contents type.

Args:

• uri: The URI of the resource (required by MCP types)

Returns:

• TextResourceContents for str content, BlobResourceContents for bytes

ResourceResult

Canonical result type for resource reads.

Provides explicit control over resource responses: multiple content items, per-item MIME types, and metadata at both the item and result level.

Methods:

to_mcp_result

to_mcp_result(self, uri: AnyUrl | str) -> mcp.types.ReadResourceResult

Convert to MCP ReadResourceResult.

Args:

• uri: The URI of the resource (required by MCP types)

Returns:

• MCP ReadResourceResult with converted contents

Resource

Base class for all resources.

Methods:

from_function

from_function(cls, fn: Callable[..., Any], uri: str | AnyUrl) -> FunctionResource

set_default_mime_type

set_default_mime_type(cls, mime_type: str | None) -> str

Set default MIME type if not provided.

set_default_name

set_default_name(self) -> Self

Set default name from URI if not provided.

read

read(self) -> str | bytes | ResourceResult

Read the resource content.

Subclasses implement this to return resource data. Supported return types:

• str: Text content
• bytes: Binary content
• ResourceResult: Full control over contents and result-level meta

convert_result

convert_result(self, raw_value: Any) -> ResourceResult

Convert a raw result to ResourceResult.

This is used in two contexts:

1. In _read() to convert user function return values to ResourceResult
2. In tasks_result_handler() to convert Docket task results to ResourceResult

Handles ResourceResult passthrough and converts raw values using ResourceResult’s normalization. When the raw value is a plain string or bytes, the resource’s own mime_type is forwarded so that ui:// resources (and others with non-default MIME types) don’t fall back to text/plain.

The resource’s component-level meta (e.g. ui metadata for MCP Apps CSP/permissions) is propagated to each content item so that hosts can read it from the resources/read response.

to_mcp_resource

to_mcp_resource(self, **overrides: Any) -> SDKResource

Convert the resource to an SDKResource.

key

key(self) -> str

The globally unique lookup key for this resource.

register_with_docket

register_with_docket(self, docket: Docket) -> None

Register this resource with docket for background execution.

add_to_docket

add_to_docket(self, docket: Docket, **kwargs: Any) -> Execution

Schedule this resource for background execution via docket.

Args:

• docket: The Docket instance
• fn_key: Function lookup key in Docket registry (defaults to self.key)
• task_key: Redis storage key for the result
• **kwargs: Additional kwargs passed to docket.add()

get_span_attributes

get_span_attributes(self) -> dict[str, Any]