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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so 'Read-only' in the description is pure repetition and earns no credit. The one genuinely new element, the 'same-target editing read receipt', is unexplained jargon — an agent cannot tell what it contains or why it matters — though the active-variant fallback behavior is useful context.

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 return content and ending with the safety flag; nothing is padded. The only blemish is the unexplained 'same-target editing read receipt' phrase, which spends words without transferring meaning.

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 present the description needn't enumerate return fields, and annotations carry the safety profile, so what remains — which resource and which variant — is covered. The residual gap is routing between this tool and preview_mockup_animation / get_mockup_animation_export.

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% and the schema already documents the variantId omission behavior, so the description's restatement of it is duplicative rather than additive. It says nothing about the projectId/generationId alias pair, which is the one parameter relationship that actually needs narrative help.

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 ('Returns') and a specific resource ('saved mockup animation state') plus the resolved variant ID, which clearly separates it from create/update/preview/export siblings by implying retrieval of persisted state. It never names a sibling explicitly, so differentiation is inferred rather than stated.

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?

'Omitting variantId reads the active variant' gives one concrete usage rule, but there is no guidance on when to choose this over preview_mockup_animation or get_mockup_animation_export, which are the obvious near-neighbors. Usage is implied by the read-only retrieval framing rather than spelled out.

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