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

With only a title annotation and no readOnly/destructive hints, the description carries the burden of behavioral disclosure. It does state the core behavior (scrolling up/down by viewport-heights), but it omits side effects or limitations such as behavior at the top/bottom of the page, whether scrolling is relative to the current position, or whether the action waits for rendering to settle. This is a reasonable but not thorough disclosure for a simple scroll operation.

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 that conveys the essential action and unit of measurement with zero filler. Every word earns its place.

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 tool with fully documented parameters, the description covers the primary action but leaves gaps: no mention of return behavior or output (no output schema exists), no mention of session applicability beyond the parameter, and no guidance on repeated or large scroll amounts. It is adequate but not complete for an agent with no other context.

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%, so all parameters (amount, direction, session_id) are already documented with defaults and formats. The description adds no new parameter-level meaning beyond restating 'up or down' and 'viewport-heights,' which the schema already captures. Baseline 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 states a specific verb ('Scroll'), a clear resource ('the page'), and a precise unit of measure ('viewport-heights'), which fully captures the tool's function. It is readily distinguishable from sibling tools like session_navigate, session_click, and session_viewport, which do not involve scrolling by viewport heights.

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 implies usage: use this tool when you need to scroll the currently active page vertically. However, it provides no explicit guidance on when to prefer this tool over alternatives, no mention of prerequisites (e.g., an active session), and no exclusions or edge-case conditions. Usage is self-evident from the action but not explicitly framed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.