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Working with Tools

# Resources as Tools

Expose resources to tool-only clients

New in version `3.0.0` Some MCP clients only support tools. They cannot list or read resources directly because they lack resource protocol support. The `ResourcesAsTools` transform bridges this gap by generating tools that provide access to your server’s resources. When you add `ResourcesAsTools` to a server, it creates two tools that clients can call instead of using the resource protocol:

- `list_resources` returns JSON describing all available resources and templates
- `read_resource` reads a specific resource by URI

This means any client that can call tools can now access resources, even if the client has no native resource support.

##
​
Basic Usage

Pass your FastMCP server to `ResourcesAsTools` when adding the transform. The generated tools route through the server at runtime, which means all server middleware — auth, visibility, rate limiting — applies to resource operations automatically, exactly as it would for direct `resources/read` calls.
`ResourcesAsTools` (and `PromptsAsTools`) should be applied to a FastMCP server instance, not a raw Provider. The generated tools call back into the server’s middleware chain at runtime, so they need a server to route through. If you want to expose only a subset of resources, create a dedicated FastMCP server for those resources and apply the transform there.

    from fastmcp import FastMCP
    from fastmcp.server.transforms import ResourcesAsTools

    mcp = FastMCP("My Server")

    @mcp.resource("config://app")
    def app_config() -> str:
        """Application configuration."""
        return '{"app_name": "My App", "version": "1.0.0"}'

    @mcp.resource("user://{user_id}/profile")
    def user_profile(user_id: str) -> str:
        """Get a user's profile by ID."""
        return f'{{"user_id": "{user_id}", "name": "User {user_id}"}}'

    # Add the transform - creates list_resources and read_resource tools
    mcp.add_transform(ResourcesAsTools(mcp))

Clients now see three tools: whatever tools you defined directly, plus `list_resources` and `read_resource`. Both generated tools are annotated with `readOnlyHint=True`, since they only read data. Clients that respect tool annotations (like Cursor) can use this to auto-confirm these tool calls without prompting the user.

##
​
Static Resources vs Templates

Resources come in two forms, and the `list_resources` tool distinguishes between them in its JSON output. Static resources have fixed URIs. They represent concrete data that exists at a known location. In the listing output, static resources include a `uri` field containing the exact URI to request. Resource templates have parameterized URIs with placeholders like `{user_id}`. They represent patterns for accessing dynamic data. In the listing output, templates include a `uri_template` field showing the pattern with its placeholders. When a client calls `list_resources`, it receives JSON like this:

    [
      {
        "uri": "config://app",
        "name": "app_config",
        "description": "Application configuration.",
        "mime_type": "text/plain"
      },
      {
        "uri_template": "user://{user_id}/profile",
        "name": "user_profile",
        "description": "Get a user's profile by ID."
      }
    ]

The client can distinguish resource types by checking which field is present: `uri` for static resources, `uri_template` for templates.

##
​
Reading Resources

The `read_resource` tool accepts a single `uri` argument. For static resources, pass the exact URI. For templates, fill in the placeholders with actual values.

    # Reading a static resource
    result = await client.call_tool("read_resource", {"uri": "config://app"})
    print(result.data)  # '{"app_name": "My App", "version": "1.0.0"}'

    # Reading a templated resource - fill in {user_id} with an actual ID
    result = await client.call_tool("read_resource", {"uri": "user://42/profile"})
    print(result.data)  # '{"user_id": "42", "name": "User 42"}'

The transform handles template matching automatically. When you request `user://42/profile`, it matches against the `user://{user_id}/profile` template, extracts `user_id=42`, and calls your resource function with that parameter.

##
​
Binary Content

Resources that return binary data (like images or files) are automatically base64-encoded when read through the `read_resource` tool. This ensures binary content can be transmitted as a string in the tool response.

    @mcp.resource("data://binary", mime_type="application/octet-stream")
    def binary_data() -> bytes:
        return b"\x00\x01\x02\x03"

    # Client receives base64-encoded string
    result = await client.call_tool("read_resource", {"uri": "data://binary"})
    decoded = base64.b64decode(result.data)  # b'\x00\x01\x02\x03'

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","contacts":" \n
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","pie-chart":" \n
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","reactive":" \n
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","team-directory-reactive":" \n
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","team-directory":" \n
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"};