Checks a checkbox or radio control using a snapshot reference or CSS selector, defaulting to the active page and session.
Check a checkbox or radio control.
| Name | Required | Description | Default |
|---|---|---|---|
| pageId | No | Defaults to the active page | |
| target | Yes | Snapshot ref (e12) or unique CSS selector | |
| sessionId | No | Defaults to the active session |
Changes observed during successful MCP inspections.
v2026.10.24Input schema / properties / pageId / descriptionPrevious value: -"Stable page ID; defaults to the session active page"New value: +"Defaults to the active page"Input schema / properties / sessionId / descriptionPrevious value: -"Optional session ID; defaults to this MCP client active session"New value: +"Defaults to the active session"Input schema / properties / target / descriptionPrevious value: -"Snapshot ref such as e12, aria-ref=e12, or a unique CSS selector"New value: +"Snapshot ref (e12) or unique CSS selector"v2026.8.14Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full disclosure burden, and it says nothing about behavior: no error semantics if the element is already checked, no note on whether change events fire, no indication that the target must come from a prior nex_browser_snapshot. Eight words cannot cover a mutation on page state.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
A single front-loaded sentence with zero filler. It is efficient, though the brevity borders on under-specification rather than tight precision.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
The tool is simple, has only three fully documented parameters and no output schema, so little is strictly required. Still, for a state-mutating browser action the description omits the snapshot-ref prerequisite and failure behavior, leaving the agent to infer the workflow from siblings.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% (pageId, target, sessionId all documented, including "Snapshot ref (e12) or unique CSS selector"), so the schema does the heavy lifting. The description adds no additional parameter meaning, which matches the baseline 3 for fully described schemas.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
"Check a checkbox or radio control" states a specific verb (check) and resource (checkbox/radio), and is distinguishable from the sibling nex_browser_uncheck by polarity. It does not explicitly name that sibling, but the operation is unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Usage is only implied by the verb; there is no statement about when to use this instead of nex_browser_uncheck, nex_browser_click, or nex_browser_select_option. An agent can infer intent from the name, but nothing in the text routes it among the many sibling interaction tools.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.