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close_tab

Close an agent-owned browser tab to clean up background tabs after work is complete. It preserves the foreground tab and refuses to close the active tab unless explicitly allowed.

Instructions

Close an agent-owned browser tab without changing the foreground tab. When to use: clean up background tabs opened by this agent after work is complete. By default, refuses to close the current active foreground tab; pass allow_active:true only when the user explicitly wants the active tab closed. Related: open_tab (create a new tab), list_tabs (find tab IDs), switch_tab (select an agent tab). Multi-agent: agent-scoped tabs; cross-agent reject with TAB_NOT_OWNED; cap configurable (default 8, 1-64). Pass tab_id only when this agent owns multiple tabs; auto-resolves otherwise. RETURNS change_report: when this tool runs, the response includes a change_report field with a compact diff of what the action mutated (URL, dialogs_opened, nodes_added, nodes_removed, attrs_changed, inputs_changed, focus_shift). Use this to learn the consequence without calling read_page next. If the report exceeds the size cap, change_report.truncated:true and change_report_hint are set; call read_page for the full state.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
clientYesAllowlisted client label. Validated against the shared v0.9.36 server/extension allowlist (see mcp/src/tools/visual-session.ts -- MCP_VISUAL_CLIENT_LABELS). Required.
tab_idNoOptional. Tab id to close. Omit when the calling agent owns exactly one tab; required to disambiguate when the agent owns multiple.
is_finalNoWhen true, the visual session clears immediately after this tool resolves. Optional (default false).
allow_activeNoWhen true, allow closing the active foreground tab. Default false protects the user-visible active tab.
visual_reasonYesShort human-readable reason shown in the overlay (for example, "Logging in to GitHub"). Required.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.9/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full behavioral burden and does so thoroughly: active-tab protection, agent-scoped ownership, cross-agent rejection with TAB_NOT_OWNED, configurable tab cap, tab_id auto-resolution, and a detailed change_report return contract including truncation behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core action and scope, then proceeds through usage, related tools, multi-agent constraints, and return behavior. Each section earns its place given the tool's complexity and the absence of annotations or an output schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with no annotations and no output schema, the description is complete enough: it covers safety, multi-agent ownership, error conditions, parameter disambiguation, and the shape of the returned change_report.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3. The description adds useful nuance beyond the schema for allow_active and tab_id, explaining when active tabs may be closed and when tab_id must be supplied, though it does not further clarify visual_reason, client, or is_final.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: "Close an agent-owned browser tab without changing the foreground tab." It immediately distinguishes the tool from siblings like open_tab, list_tabs, and switch_tab by naming them in a Related section.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives explicit when-to-use guidance: clean up background tabs after work is complete. It also states the default refusal to close the active tab and the narrow condition for allow_active:true, plus related alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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