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Tool blocking lets you control exactly what your AI agent can do — hiding entire tools from view, or stopping specific requests before they execute.

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Disable specific tools

Use Hook_Filter with a disabled list to hide tools the AI should never use. Disabled tools don’t appear in the AI’s tool list at all — it can’t call what it can’t see. Example — prevent the AI from deleting calendar events or sending emails: 
{ "disabled": ["delete_event", "draft_gmail_message"] }
Ask the Configurator Agent:
“Hide the delete_event tool on my Google Calendar server”
“Remove send capabilities from Gmail — draft only”

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Whitelist: only allow specific tools

Use an enabled list to restrict a server to exactly the tools you want. Every other tool on that server is hidden. Example — lock GitHub to read-only operations: 
{ "enabled": ["get_repository", "list_issues", "search_repositories", "get_pull_request"] }
“Limit my GitHub server to search and read tools only”
Whitelisting is the safer default for production agents — you explicitly opt in to each capability rather than blocking known risks.

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Block by parameter pattern

Request guardrails block tool calls when an input matches a pattern — even if the tool itself is visible. Example — block GitHub code searches for secrets:
“Add a guardrail to block code searches containing ‘password’, ‘api_key’, or ‘secret’”
Example — prevent SQL queries that drop or truncate tables:
“Block any PostgreSQL query containing DROP TABLE or TRUNCATE”

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Common blocking patterns by server

ServerRecommended blocks
google-calendardelete_event, modify_event (attendee changes)
google-gmaildelete_gmail_filter, create_gmail_filter
google-driveany file deletion tools
google-docsfind_and_replace_doc (bulk destructive)
github-remotedelete_repository, delete_branch
postgres / mysqlDROP, TRUNCATE, DELETE without WHERE
slackdelete_message, kick_user_from_channel

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Blocking vs revocation

Blocking (via guardrails) hides or restricts a tool while keeping the server connection intact. Revocation severs the connection entirely. Use blocking for ongoing least-privilege configuration. Use revocation when responding to an incident.

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How to configure

Ask the Configurator Agent in Civic Chat, or configure directly in the Civic UI under your toolkit’s guardrail settings. 
Action: update
Category: Hook_Filter
MCP Server: google-calendar
Value: { "disabled": ["delete_event"] }