This record as markdown: /tools/browser/close-tab.md
What close_tab does on Browser
AI agents call close_tab to permanently remove resources in Browser, typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.
Why close_tab is rated Critical
Closing a tab cannot be undone; any unsaved form data, page state, or session information is permanently lost. While not as severe as deleting files or dropping databases, it is an irreversible action that could disrupt ongoing user sessions or lose work. Severity is medium because blast radius is limited to a single browser tab.
From the tool's definition 'Close tab' - closing a browser tab is an irreversible action that destroys the tab's state, session, and any unsaved content
Attacks that exploit this kind of access
The rule that runs close_tab safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Browser, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For close_tab, this is the rule to start with:
close_tab is removed from the agent's tool list entirely, so the agent never calls it. The rest of the server keeps working.
The button opens the PolicyLayer dashboard: create your workspace, connect Browser, apply this rule, and every close_tab call is checked against it from then on.
Questions about close_tab
Close tab (tab id). It is categorised as a Destructive tool in the Browser MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.
Register the Browser MCP server in PolicyLayer and add a rule for close_tab: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Browser. Nothing to install.
close_tab is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the close_tab rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for close_tab. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
close_tab is provided by the Browser MCP server (mcp-server-browser). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
More on Browser, and thousands of servers like it.
Across the catalogue