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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so the mutation profile is partly covered. The description adds real value beyond that: the partial-update semantics, the non-obvious side effect that changing the look restyles every scene via shared CSS variables, and the required scopes demos:read and demos:write.

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?

Very compact — three short sentences plus a scope line, with the side-effect warning and permission requirement clearly separated. The opening sentence is a dangling fragment with no verb, which costs a point on structure but not on brevity.

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?

Given 7 parameters, nested objects, no output schema, and a sibling set full of downstream generators, the definition covers mutation semantics, the restyle side effect and auth. It omits what happens to derived artifacts (e.g., whether voiceovers must be regenerated with generate_video_voiceovers) and any mention of invalid-id or validation failure behavior.

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 14% (only videoId is documented), so the description must carry the load; it does partially by enumerating the top-level fields and the look sub-fields. It still adds no meaning to nested options such as music.duck, voice.speed, captions.style, or the individual color roles, so the compensation is incomplete.

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?

The description enumerates the exact video-level attributes that can be changed (title, aspect, look with its preset/colors/fonts/motif/pace/radius sub-fields, captions, voice, music), which is a specific resource+operation. It is grammatically a fragment with no verb, relying on the name/title to supply 'update', but the field inventory still lets an agent distinguish it from scene-level edits like update_scene or replace_video_text.

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?

'Only the fields you send change' clearly communicates partial-update usage, which is genuinely useful guidance. However, there is no explicit when-to-use versus siblings (update_scene, replace_video_text, update_brand_kit) and no guidance on follow-up steps such as regenerating voiceovers after a voice change.

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