animations

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

Adds behavior well beyond the annotations: it refuses on a hidden page, warns that composited_estimate is a guess rather than the compositor's answer, defines fade_only, and explains the 150 ms-transition timing rationale for recording. Annotations declare readOnlyHint=false and idempotentHint=false, which is consistent with the fact that it can trigger click/hover/scroll/press_key actions.

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 capability and output shape, then the two operating modes, then caveats. Dense semicolon-clause sentences pack substantial information with little waste, though the length pushes toward run-on territory.

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 carries the burden of explaining return values and does so (selector/ref, animated properties, duration, delay, easing, iterations, play state, timeline, composited_estimate, fade_only). It also covers the hidden-page refusal and the reduced-motion workflow. Minor gap: it does not describe the limit/summary interaction that the schema implies.

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 goes further by explaining the semantic split between snapshot mode and duration_ms recording mode, and by clarifying that optionally an action runs after recording starts. This adds meaning about how parameters interact rather than restating field text.

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 and resource ("List the page animations") and enumerates the four animation technologies it covers (CSS animations, transitions, Web Animations, View Transitions), plus the per-item fields it returns. An agent can distinguish this from get_css_styles or watch_dom without opening the 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 partitions two modes: without duration_ms it is a snapshot of what runs now; with duration_ms it records every animation that starts in the window, optionally after an action. It also routes for a related task ("Pair with emulate_media reducedMotion"). It does not explicitly contrast with sibling listing tools like get_css_styles, so it stops short of a full when/when-not statement.

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