animations

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

Adds real behavioral context beyond the annotations: it discloses that recording runs an optional action (hover/click/scroll/key), that composited_estimate is only a guess rather than the compositor's answer, what fade_only means for prefers-reduced-motion, and that it refuses on a hidden page. No contradiction with the declared hints.

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-loads the resource and its categories, then the mode switch. It is a dense single paragraph with heavy punctuation, but nearly every clause carries load and nothing is repeated from structured fields.

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 no output schema, the description compensates by naming the returned fields (selector, ref, animated properties, duration, delay, easing, iterations, play state, timeline, composited_estimate, fade_only). Combined with mode behavior and the hidden-page constraint, an agent has everything needed to call it correctly.

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, but the description adds meaning the schema lacks: the temporal rationale for duration_ms ('a 150 ms transition is over before a second call') and the action trigger set (hover, click, scroll, key). It does not explain tab_id/frame_id resolution beyond the schema.

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?

States a specific verb ('List') and resource ('page animations') and enumerates the exact categories covered: CSS animations, transitions, Web Animations, and View Transitions. An agent can distinguish this from siblings like get_css_styles or track_events without opening a schema.

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?

Clearly routes between modes ('Without duration_ms: what runs now. With duration_ms: records every animation that starts in the window') and names alternatives with conditions: pair with emulate_media reducedMotion for the reduced version, and note that frames handles smoothness. It also states the hidden-page refusal up front.

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