Close a specific browser tab by its stable page ID to manage active sessions and free resources. Ideal for automated tab cleanup without disrupting other tabs.
Close a tab by stable page ID.
| Name | Required | Description | Default |
|---|---|---|---|
| pageId | Yes | ||
| sessionId | No | Optional session ID; defaults to this MCP client active session |
Changes observed during successful MCP inspections.
v2026.8.14Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotation destructiveHint: true already signals that this operation is destructive. The description adds the qualifier 'stable' to page ID, which provides context about the nature of the identifier. However, it does not disclose any additional behavioral traits such as side effects on the browser session or what happens when closing the last tab. The description is consistent with annotations, so no contradiction.
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?
The description is a single, focused sentence that conveys the essential action and required parameter without any wasted words. It is extremely concise and front-loaded.
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?
For a destructive tool with no output schema, the description is minimally sufficient: it states the action and the primary parameter. However, it lacks context such as how to get a valid page ID, potential errors, or behavior when the tab is the last one. The presence of sibling tools like tab_list partially mitigates this, but the description itself does not reference them.
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?
The input schema describes sessionId but leaves pageId undocumented (50% coverage). The description clarifies that pageId is a 'stable' identifier, adding meaning beyond the plain 'string' type. However, it doesn't explain where to obtain the page ID or the relationship between pageId and sessionId, so it only partially compensates for the schema gap.
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?
The description clearly states the action ('Close'), the target resource ('a tab'), and the method ('by stable page ID'). It distinguishes from sibling tools like nex_browser_close (which likely closes the entire browser) and tab management tools (tab_new, tab_select).
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?
The description provides no guidance on when to use this tool versus alternatives. It does not mention when to use nex_browser_close instead, nor any prerequisites like needing to obtain the page ID from tab_list. There is no implied context beyond the basic operation.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.