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

Goes beyond the readOnly/destructive annotations by disclosing the 400 ms UI cap and how allow_long lifts it, and by warning that the formula is a proprietary heuristic to tune by eye rather than a standard. That caveat meaningfully changes how an agent should present the result; it only lacks detail on precision/rounding of outputs.

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 verb phrase, then parameters, then returns, then the caveat in a single closing clause. Dense but every sentence carries information; nothing is redundant with the schema.

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?

There is no output schema, so the description carries the return contract — it names the recommended duration, the enter/exit pair, a five-step token scale and the rationale. Combined with the disclosed cap and heuristic caveat, an agent can call this and explain the result without further information.

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 already 100%, so the baseline is 3, and the description still adds value: it gives the 0–5000 range for distance_px inline, clarifies that size means the element's size, and motivates allow_long with concrete use cases rather than repeating the terse schema 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+resource ('Plan animation durations') and enumerates the inputs and return values, so the agent knows exactly what it computes. It doesn't explicitly distinguish itself from nearby siblings such as design_easing, plan_stagger or check_motion, which is the only thing keeping it off a 5.

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?

Usage is implied by the input vocabulary (distance, size, complexity) and there is an explicit condition for the optional flag ('allow_long ... for decorative or page-level motion'), but there is no statement of when to reach for this versus design_easing or plan_stagger, and no exclusions.

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