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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true, so safety is partly covered; the description still adds real context beyond them by disclosing that the call spends planning credits, what it returns (scene narration, factual review notes, references, credit estimate), and that it does not generate images or animate video. 'Existing account access applies' gestures at auth requirements but is too vague to fully discharge them.

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 purpose and the credit cost, with no wasted prose. The closing 'Existing account access applies' is vague filler that adds little, keeping it out of 5 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?

An output schema exists, so the description needn't explain return values (though it partially does), and annotations cover the safety profile. For a 19-parameter mutation that spends credits, however, the near-total absence of parameter guidance leaves the definition only minimally complete for correct invocation.

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 description coverage is only 5% across 19 parameters, so the description carries the burden of explaining them — and it barely does, covering only the script ('user-approved script') and implicitly the project. Undocumented inputs such as video_model, voice_id, visual_style, character_ids, story_kit_id and target_duration_seconds are left for the agent to guess at.

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 ('Create a vertical video storyboard') plus scope ('for the user-approved script in an existing project'). The negative scope statement ('Does not generate images or animate video') separates it from generation_video_create and the generation_* siblings, and the name/title disambiguate it from video_storyboard_revise and video_storyboard_approve.

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?

It gives a clear precondition (user-approved script, existing project) and a clear exclusion (not image generation or video animation), which tells the agent when this is the right call. It stops short of naming the alternative siblings (e.g. video_storyboard_revise for an already-created storyboard), so no explicit routing.

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