Scroll a specified browser tab's viewport by horizontal and vertical deltas, enabling precise navigation and content inspection.
Scroll the active tab viewport by deltaX and deltaY.
| Name | Required | Description | Default |
|---|---|---|---|
| tab_id | Yes | The ID of the tab | |
| delta_x | No | Horizontal scroll amount | |
| delta_y | No | Vertical scroll amount |
Changes observed during successful MCP inspections.
v1.2.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description must disclose behavior on its own. It only states that scrolling happens by the given deltas, without covering whether changes are temporary, whether any permissions are needed, whether the tab must be active, or what the tool returns. This leaves notable behavioral gaps for a simple but observable browser action.
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, compact sentence with no filler. It front-loads the action and resource, though the 'active tab' phrasing could have been omitted or clarified to avoid redundancy with the required tab_id.
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 simple scroll operation with a fully described schema, the description covers the primary action. Still, it omits the active-tab ambiguity, what happens after the call (return value or lack thereof), and any context about whether the viewport belongs to the specified tab. These gaps keep it from being fully complete.
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 already has 100% coverage with descriptions for all parameters. The description repeats the delta names but adds no new semantic context (e.g., coordinate system, sign conventions, bounds). According to the baseline for high schema coverage, a 3 is appropriate.
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 verb ('Scroll') and the resource ('active tab viewport'), and it names the two delta parameters. It is the only scroll tool among the siblings, so it differentiates itself naturally. However, the phrase 'active tab viewport' is slightly ambiguous because the schema requires a tab_id and does not explicitly say the tab must be active.
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 gives no guidance on when to use this tool versus the many siblings, such as get_snapshot or execute_script as alternatives for programmatic scrolling. There is no mention of prerequisites like the tab being active or focused, and no exclusions or fallback suggestions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.