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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the safety profile is covered. The description usefully discloses the deferred-effect mechanism (prompts are re-written so the clip later speaks the line), but never states what the destructive flag actually destroys here — the existing narration/rendered audio — nor any credit cost implied by the required regenerate step. Adds real context, but leaves the destructive semantics unstated.

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?

Two sentences, purpose front-loaded, no filler. The second sentence's punctuation (a colon introducing both a preferred alternative and a separate follow-up workflow) is slightly tangled and costs a re-read, but the content is dense and earns its place.

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?

For a three-required-param tool with full schema coverage and no output schema, the description supplies the key operational facts: the redirect to edit_scene and the mandatory regenerate_scene step on rendered videos. It stops short of noting cost/credit implications of that regeneration, which an agent would want before acting.

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 all three params are documented in-schema with sourcing hints (scene_id from get_video, video_id from create_video/list_videos/get_video). The description only restates the narration parameter implicitly ('the new spoken line'), adding no syntax or constraint detail beyond the maxLength=800 already in the schema. Baseline 3 applies.

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 ('Change one scene's spoken line') in one clear sentence, and explicitly positions it against the sibling edit_scene(narration=...) which it says is preferred. An agent can distinguish it from edit_scene and regenerate_scene without opening a schema.

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?

Gives an explicit preferred alternative ('Same as edit_scene(narration=...), which is preferred') and a conditional follow-up rule ('on a rendered video, apply it with regenerate_scene(mode='narration')'). Both when-to-use and what-else-to-use are named, not implied.

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