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fastmcp.utilities.visibility

Visibility filtering for FastMCP components. This module provides the VisibilityFilter class which handles blocklist and allowlist logic for controlling component visibility at both the provider and server levels.

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Classes

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VisibilityFilter

Manages component visibility with blocklist and allowlist support. Both servers and providers use this class to control which components are visible. 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.