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

Annotations already declare readOnlyHint=false and openWorldHint=true, so the agent knows this is a state-changing operation. The description adds behavioral context: it triggers lazy-loaded content, may require a follow-up snapshot, and notes that click auto-scrolls. This enriches the understanding of side effects without contradicting annotations.

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?

Three concise paragraphs, each earning its place: the first states the core function, the second gives the primary use case and post-action step, the third clarifies when to use alternatives. No filler or repetition.

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 two-parameter tool with full schema coverage, an output schema, and clear annotations, the description covers the essential context: what it does, when to use it, what to do after, and how it relates to sibling tools. This is complete for an agent to correctly invoke it.

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 coverage is 100%, with descriptions for both 'amount' and 'direction' that fully explain their format and defaults (e.g., '25 is a quarter screen'). The tool description adds no new parameter semantics beyond what the schema already provides, so the baseline of 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 starts with a specific verb and resource: 'Scroll the page up or down by a percentage of the viewport.' It clearly distinguishes itself from siblings like scroll_to_selector and click by stating its scope (percentage-based scrolling) and its role as the tool for infinite scroll.

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?

Explicit guidance is given: it is 'The way to trigger lazy-loaded content and infinite scroll,' and the description advises taking a take_snapshot afterwards. It also explicitly excludes alternatives: 'scroll_to_selector is more precise' for known elements, and 'click already scrolls to its target,' so no pre-scroll is needed. This gives clear when-to-use and when-not-to-use context.

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