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check_box

Check or uncheck a page checkbox or toggle switch, returning the new checked state. Use after locating its selector to verify form inputs and custom switches.

Instructions

Toggle a checkbox element. Returns the new checked state. When to use: to check or uncheck form checkboxes or toggle switches. Related: get_dom_snapshot (find checkbox selectors), click (alternative for custom checkbox UI components). 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 this action targets. Omit when the calling agent owns exactly one tab; pass to disambiguate when the agent owns multiple. Single-tab agents and legacy popup/sidepanel/autopilot do not need to pass this.
is_finalNoWhen true, the visual session clears immediately after this tool resolves. Optional (default false).
selectorYesCSS selector or element reference for the checkbox
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

A4.6/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden and delivers: agent-scoped tab ownership, the TAB_NOT_OWNED cross-agent rejection, a configurable concurrency cap (default 8, range 1-64), and a detailed change_report return contract including truncation signaling. This is unusually rich behavioral disclosure for a mutation tool.

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

Conciseness4/5

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

Front-loaded with purpose and return value, then organized into labeled blocks (When to use / Related / Multi-agent / RETURNS). It is dense and slightly repetitive on tab_id ownership, but nearly every sentence carries actionable information, especially the change_report contract that no output schema covers.

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?

No output schema exists, yet the description fully specifies the return value (new checked state plus change_report fields) and its truncation escape hatch. Combined with the multi-agent and cap behavior, an agent has everything needed to invoke this correctly.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents all five parameters, including tab_id's single-vs-multi-tab rule. The description restates the tab_id guidance rather than adding new syntax or format detail, so baseline 3 applies.

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?

States a specific verb and resource ('Toggle a checkbox element') and immediately names the return ('Returns the new checked state'). It also distinguishes itself from siblings by naming get_dom_snapshot for selector discovery and click as the alternative for custom checkbox UI.

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?

Explicit 'When to use' clause covers both checkboxes and toggle switches, and the 'Related' section names two alternatives with the condition that selects each (get_dom_snapshot to find selectors, click for custom components). Nothing is left to inference.

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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