fastmcp.resources.base

Base classes and interfaces for FastMCP resources.

Functions

convert_raw_to_resource_result ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L270" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

convert_raw_to_resource_result(raw_value: Any) -> ResourceResult

Wrap a user function's return value in a ResourceResult.

Shared by Resource and ResourceTemplate so both honor the MIME type the component declares in listings. A component that advertises text/csv must not serve text/plain on read.

Args:

• raw_value: The value returned by the user's function.
• mime_type: The component's declared MIME type, forwarded to content items.
• meta: Component-level meta (e.g. ui metadata for MCP Apps CSP/permissions) propagated to each content item.

Classes

ResourceContent ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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 ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L89" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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 ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L116" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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 ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L197" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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

InputRequiredResourceResult ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L213" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

The full result of a single multi-round-trip resource read (SEP-2322).

InputRequiredResult is a result type, not a tools/call feature: any request may resolve to one. When a resource or resource template returns an InputRequiredResult from its body to ask the client for input, that ask is the legitimate result of this resources/read — so FastMCP wraps it in this ResourceResult subclass, mirroring InputRequiredToolResult and InputRequiredPromptResult, and it flows through the middleware chain as an ordinary return value.

Invariant: the wrapped InputRequiredResult is never serialized as resource contents. contents is always empty; the wire handler (_on_read_resource) reads .input_required and returns it to the runner.

Resource ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L334" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

Base class for all resources.

Methods:

from_function ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L359" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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

set_default_mime_type ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L396" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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

Set default MIME type if not provided.

set_default_name ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L403" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

set_default_name(self) -> Self

Set default name from URI if not provided.

read ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L413" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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 ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L425" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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 ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L457" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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

Convert the resource to an SDKResource.

key ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L480" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

key(self) -> str

The globally unique lookup key for this resource.

get_span_attributes ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/resources/base.py#L485" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

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