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

Annotations already declare readOnlyHint=true and destructiveHint=false, so 'Does not modify the design' largely restates structured data. The genuinely additive content is the clarification of the times unit, though the description does not explain how the PNGs are returned or why idempotentHint is false for a deterministic render.

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 short sentences, front-loaded with the action and output, then the one non-obvious parameter caveat, then the safety note. No filler.

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 should say more about the return value than 'PNG inspection images' — e.g. whether images come back inline, as URLs, or as asset references, and how the four-frame cap interacts with the times array. The unit clarification is good, but the return contract is thin.

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 75%, and the description adds real meaning the schema lacks: 'times are timeline seconds within motionDuration, not normalized keyframe fractions' resolves a genuine ambiguity in the times array. It does not touch scale or variantId, but those are already documented in 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 and resource ('Renders ... frames of a saved mockup animation') plus the output form ('PNG inspection images'). It implicitly separates itself from export_mockup_animation via 'inspection images', but never names that sibling, so the differentiation is left to inference.

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?

The word 'inspection' hints at preview-before-export usage, but there is no explicit when-to-use, when-not-to-use, or named alternative such as export_mockup_animation or get_mockup_animation. The agent must infer the routing.

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