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

Annotations already declare idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds value beyond them by disclosing that this costs nothing ('No generation or charge'), that it targets an already-existing line, and the default sync value per line type - all relevant to a mutating tool.

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?

Four short sentences with no filler: identity/scope first, then the parameter meaning, then defaults, then the cost guarantee. Each sentence carries information an agent would otherwise have to guess.

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 7-parameter mutation with an output schema available, the description covers what changes, the target, defaults and cost. It is thin on what happens when the precondition fields (expectedText, expectedStartMs, revisionId) do not match, and on how it differs from studio_film_set_lip_sync, which is the main residual gap.

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 71%, so the schema carries most parameter detail, but the description still adds meaning: sync:true is defined behaviorally (the artist mouths the line) and the defaulting rule is explained, which the schema's one-line sync description does not cover. It does not clarify the precondition parameters (revisionId, expectedText, expectedStartMs) beyond the schema text.

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 with scope: 'Sets lip-sync for one existing lyric line identified by section index and stable line ID.' The 'one existing lyric line' phrasing separates it from line-creation tools, but it never names or contrasts with the close sibling studio_film_set_lip_sync, so an agent must infer the boundary.

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 conveys useful context - defaults are true for the artist's own words and false for guest/ad-lib lines, and there is no generation or charge - but gives no explicit when-to-use/when-not-to-use direction or an alternative tool to pick instead. Usage is implied rather than stated.

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