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fastmcp.server.transforms.visibility

Visibility transform for filtering components based on enable/disable settings. This module provides the Visibility class which manages component visibility with blocklist and allowlist support. Components can be hidden by key or tag, and the visibility state is mutable - changes take effect on subsequent queries.

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Classes

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Visibility

Filters components based on visibility settings. Manages blocklist and allowlist logic for controlling component visibility. Both servers and providers use this class. Visibility is hierarchical: if a component is hidden at any level (provider or server), it’s hidden to the client. Filtering logic (blocklist wins over allowlist):
  1. If component key is in _disabled_keys → HIDDEN
  2. If any component tag is in _disabled_tags → HIDDEN
  3. If _default_enabled is False and component not in allowlist → HIDDEN
  4. Otherwise → VISIBLE
The only=True flag on enable() switches to allowlist mode:
  • Sets _default_enabled = False
  • Clears existing allowlists
  • Adds specified keys/tags to allowlist
Methods:

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disable 

disable(self) -> None
Add to blocklist (hide components). Args:
  • keys: Component keys to hide (e.g., “tool:my_tool@”, “resource:file://x@”)
  • tags: Tags to hide - any component with these tags will be hidden

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enable 

enable(self) -> None
Remove from blocklist, or set allowlist with only=True. Args:
  • keys: Component keys to show
  • tags: Tags to show
  • only: If True, switches to allowlist mode - ONLY show these keys/tags. This sets default visibility to False, clears existing allowlists, and adds the specified keys/tags to the allowlist.

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reset 

reset(self) -> None
Reset to default state (everything enabled, no filters).

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is_enabled 

is_enabled(self, component: FastMCPComponent) -> bool
Check if component is enabled. Blocklist wins over allowlist.

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list_tools 

list_tools(self, call_next: ListToolsNext) -> Sequence[Tool]
Filter tools by visibility.

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get_tool 

get_tool(self, name: str, call_next: GetToolNext) -> Tool | None
Get tool if enabled, None otherwise.

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list_resources 

list_resources(self, call_next: ListResourcesNext) -> Sequence[Resource]
Filter resources by visibility.

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get_resource 

get_resource(self, uri: str, call_next: GetResourceNext) -> Resource | None
Get resource if enabled, None otherwise.

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list_resource_templates 

list_resource_templates(self, call_next: ListResourceTemplatesNext) -> Sequence[ResourceTemplate]
Filter resource templates by visibility.

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get_resource_template 

get_resource_template(self, uri: str, call_next: GetResourceTemplateNext) -> ResourceTemplate | None
Get resource template if enabled, None otherwise.

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list_prompts 

list_prompts(self, call_next: ListPromptsNext) -> Sequence[Prompt]
Filter prompts by visibility.

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get_prompt 

get_prompt(self, name: str, call_next: GetPromptNext) -> Prompt | None
Get prompt if enabled, None otherwise.