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

Annotations already declare openWorldHint=true and readOnlyHint=false, so the open-web, write-side nature is known. The description usefully adds the auth requirement (write scope) and output shape, but its claim 'Free: nothing is charged' directly conflicts with the budgetUsd parameter that defaults to 2 with a max of 10, leaving real cost behavior ambiguous.

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?

Front-loaded with the core action and return value, and each short sentence covers a distinct fact (output, duration heuristic, cost, scope). The cost sentence is the one weak link because it is misleading rather than merely extra.

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?

With an output schema and full annotation coverage, the description only needs to carry the action, the auth requirement, and call-shaping hints — all present. The remaining gap is routing guidance against the many sibling capture/read tools and the unresolved cost statement.

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%, so the baseline is 3. The description adds one genuinely useful heuristic — 8 to 15 seconds reads as one shot — that guides duration_seconds, but the 'nothing is charged' line muddies rather than clarifies budgetUsd.

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 names a concrete verb and resource — a real browser opens a URL and scrolls it top to bottom — and states the produced artifact (an MP4 media key plus its first frame). That framing clearly separates it from read_page, screenshot_page, and demo_page without needing the schema opened.

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?

It gives an implicit usage tip (8-15 seconds reads as one shot) and a prerequisite (needs the write scope), which helps an agent call it correctly. But it never says when to choose this over screenshot_page/read_page/demo_page, and gives no when-not conditions.

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