base

fastmcp.server.providers.base

Base Provider class for dynamic MCP components.

This module provides the Provider abstraction for providing tools, resources, and prompts dynamically at runtime.

Example:

from fastmcp import FastMCP
from fastmcp.server.providers import Provider
from fastmcp.tools import Tool

class DatabaseProvider(Provider):
    def __init__(self, db_url: str):
        super().__init__()
        self.db = Database(db_url)

    async def _list_tools(self) -> list[Tool]:
        rows = await self.db.fetch("SELECT * FROM tools")
        return [self._make_tool(row) for row in rows]

    async def _get_tool(self, name: str) -> Tool | None:
        row = await self.db.fetchone("SELECT * FROM tools WHERE name = ?", name)
        return self._make_tool(row) if row else None

mcp = FastMCP("Server", providers=[DatabaseProvider(db_url)])

Classes

Provider

Base class for dynamic component providers.

Subclass and override whichever methods you need. Default implementations return empty lists / None, so you only need to implement what your provider supports.

Methods:

transforms

transforms(self) -> list[Transform]

All transforms applied to components from this provider.

add_transform

add_transform(self, transform: Transform) -> None

Add a transform to this provider.

Transforms modify components (tools, resources, prompts) as they flow through the provider. They’re applied in order - first added is innermost.

Args:

• transform: The transform to add.

wrap_transform

wrap_transform(self, transform: Transform) -> Provider

Return a new provider with this transform applied (immutable).

Unlike add_transform() which mutates this provider, wrap_transform() returns a new provider that wraps this one. The original provider is unchanged.

This is useful when you want to apply transforms without side effects, such as adding the same provider to multiple aggregators with different namespaces.

Args:

• transform: The transform to apply.

Returns:

• A new provider that wraps this one with the transform applied.

list_tools

list_tools(self) -> Sequence[Tool]

List tools with all transforms applied.

Applies transforms sequentially: base → transforms (in order). Each transform receives the result from the previous transform. Components may be marked as disabled but are NOT filtered here - filtering happens at the server level to allow session transforms to override.

Returns:

• Transformed sequence of tools (including disabled ones).

get_tool

get_tool(self, name: str, version: VersionSpec | None = None) -> Tool | None

Get tool by transformed name with all transforms applied.

Note: This method does NOT filter disabled components. The Server (FastMCP) performs enabled filtering after all transforms complete, allowing session-level transforms to override provider-level disables.

Args:

• name: The transformed tool name to look up.
• version: Optional version filter. If None, returns highest version.

Returns:

• The tool if found (may be marked disabled), None if not found.

get_app_tool

get_app_tool(self, app_name: str, tool_name: str) -> Tool | None

Look up an app-visible tool by original name, bypassing transforms.

Searches for a tool named tool_name tagged with the given app name. Skips the transform chain entirely.

Returns:

• The tool if found and tagged with the given app name, else None.

list_resources

list_resources(self) -> Sequence[Resource]

List resources with all transforms applied.

Components may be marked as disabled but are NOT filtered here.

get_resource

get_resource(self, uri: str, version: VersionSpec | None = None) -> Resource | None

Get resource by transformed URI with all transforms applied.

Note: This method does NOT filter disabled components. The Server (FastMCP) performs enabled filtering after all transforms complete.

Args:

• uri: The transformed resource URI to look up.
• version: Optional version filter. If None, returns highest version.

Returns:

• The resource if found (may be marked disabled), None if not found.

list_resource_templates

list_resource_templates(self) -> Sequence[ResourceTemplate]

List resource templates with all transforms applied.

Components may be marked as disabled but are NOT filtered here.

get_resource_template

get_resource_template(self, uri: str, version: VersionSpec | None = None) -> ResourceTemplate | None

Get resource template by transformed URI with all transforms applied.

Note: This method does NOT filter disabled components. The Server (FastMCP) performs enabled filtering after all transforms complete.

Args:

• uri: The transformed template URI to look up.
• version: Optional version filter. If None, returns highest version.

Returns:

• The template if found (may be marked disabled), None if not found.

list_prompts

list_prompts(self) -> Sequence[Prompt]

List prompts with all transforms applied.

Components may be marked as disabled but are NOT filtered here.

get_prompt

get_prompt(self, name: str, version: VersionSpec | None = None) -> Prompt | None

Get prompt by transformed name with all transforms applied.

Note: This method does NOT filter disabled components. The Server (FastMCP) performs enabled filtering after all transforms complete.

Args:

• name: The transformed prompt name to look up.
• version: Optional version filter. If None, returns highest version.

Returns:

• The prompt if found (may be marked disabled), None if not found.

get_tasks

get_tasks(self) -> Sequence[FastMCPComponent]

Return components that should be registered as background tasks.

Override to customize which components are task-eligible. Default calls list_* methods, applies provider transforms, and filters for components with task_config.mode != ‘forbidden’.

Used by the server during startup to register functions with Docket.

lifespan

lifespan(self) -> AsyncIterator[None]

User-overridable lifespan for custom setup and teardown.

Override this method to perform provider-specific initialization like opening database connections, setting up external resources, or other state management needed for the provider’s lifetime.

The lifespan scope matches the server’s lifespan - code before yield runs at startup, code after yield runs at shutdown.

enable

enable(self) -> Self

Enable components matching all specified criteria.

Adds a visibility transform that marks matching components as enabled. Later transforms override earlier ones, so enable after disable makes the component enabled.

With only=True, switches to allowlist mode - first disables everything, then enables matching components.

Args:

• names: Component names or URIs to enable.
• keys: Component keys to enable (e.g., ).
• version: Component version spec to enable (e.g., VersionSpec(eq=“v1”) or VersionSpec(gte=“v2”)). Unversioned components will not match.
• tags: Enable components with these tags.
• components: Component types to include (e.g., ).
• only: If True, ONLY enable matching components (allowlist mode).

Returns:

• Self for method chaining.

disable

disable(self) -> Self

Disable components matching all specified criteria.

Adds a visibility transform that marks matching components as disabled. Components can be re-enabled by calling enable() with matching criteria (the later transform wins).

Args:

• names: Component names or URIs to disable.
• keys: Component keys to disable (e.g., ).
• version: Component version spec to disable (e.g., VersionSpec(eq=“v1”) or VersionSpec(gte=“v2”)). Unversioned components will not match.
• tags: Disable components with these tags.
• components: Component types to include (e.g., ).

Returns:

• Self for method chaining.