Switch to a specific browser tab on a mobile device using its serial number and tab ID, returning the API response.
Focus one tab.
Args: serialno: The browser device serialno, from list_devices. tab_id: The tab id, from browser_tabs.
Returns: JSON response from the API.
| Name | Required | Description | Default |
|---|---|---|---|
| tab_id | Yes | ||
| serialno | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v0.2.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden of disclosing behavior. It only states the action and a vague return type ('JSON response from the API'). It does not mention side effects (e.g., whether the current tab is closed), prerequisites, reversibility, or error handling. This is a significant gap for a tool that changes browser 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?
The description is extremely concise and front-loaded with the main purpose. However, it is so brief that it lacks essential behavioral context. While it follows a clear Args/Returns structure, the content is sparse. It is not verbose, but it under-specifies, which is not a positive form of conciseness.
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 tool with two simple parameters and no annotations, the description is incomplete. It does not explain what the returned JSON contains, what errors might occur, or what happens to the previous tab. Even though the operation is conceptually simple, the lack of any output schema description or behavioral details makes it insufficient for an agent to call it confidently.
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 schema has no descriptions for parameters (0% coverage), so the description must compensate. It adds the source of each parameter ('from list_devices' and 'from browser_tabs'), which is useful. However, it does not explain the format or constraints of tab_id (e.g., whether it is an index or a handle), leaving room for ambiguity. The added value is minimal beyond schema titles.
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 states a clear action ('Focus one tab') with a specific resource (a browser tab). It is not a tautology and is distinct from sibling actions like open/close. However, it does not explicitly contrast with siblings such as browser_tab_open or browser_tab_close, so it falls short of a 5.
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 minimal usage context by noting that tab_id comes from browser_tabs and serialno from list_devices, but it gives no guidance on when to use this tool versus alternatives (e.g., browser_tab_open to create a new tab). There are no exclusions or conditions for selection, leaving the agent to infer usage.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.