fastmcp/docs/python-sdk/fastmcp-resources-base.mdx

---
title: base
sidebarTitle: base
---

# `fastmcp.resources.base`


Base classes and interfaces for FastMCP resources.

## Functions

### `convert_raw_to_resource_result` <sup><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></sup>

```python
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` <sup><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></sup>


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` <sup><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></sup>

```python
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` <sup><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></sup>


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` <sup><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></sup>

```python
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` <sup><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></sup>


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` <sup><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></sup>


Base class for all resources.


**Methods:**

#### `from_function` <sup><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></sup>

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

#### `set_default_mime_type` <sup><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></sup>

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

Set default MIME type if not provided.


#### `set_default_name` <sup><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></sup>

```python
set_default_name(self) -> Self
```

Set default name from URI if not provided.


#### `read` <sup><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></sup>

```python
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` <sup><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></sup>

```python
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` <sup><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></sup>

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

Convert the resource to an SDKResource.


#### `key` <sup><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></sup>

```python
key(self) -> str
```

The globally unique lookup key for this resource.


#### `get_span_attributes` <sup><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></sup>

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