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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is partly covered. The description adds real value beyond them: it explains the cascade to later scenes, the 4–30s normalization/clamping, the idempotent retry reconciliation via operationId, and the absence of billing — details an agent cannot infer from the annotations alone.

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, front-loaded with the core action and its normalization/cascade effect, then the revision/operationId contract and cost note. No filler, and each clause carries distinct information.

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 mutation with an output schema and full annotation coverage, the description supplies the missing pieces an agent needs: downstream scene effects, clamping behavior, concurrency via expectedRevision, idempotent retries, and zero cost. Return-value explanation is unnecessary given the output schema.

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 100%, so a baseline of 3 applies. The description goes further by explaining the relationship between expectedRevision (current saved plan revision) and operationId (identical retries reconcile to the same edit), which adds semantic meaning about concurrency and idempotency beyond the individual field docs.

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 (set one scene's duration) and immediately scopes behavior: normalization to 4–30 seconds with later scenes following. This is distinguishable from generic siblings like studio_film_scenes_write or studio_film_edit_line, which have no such duration-specific normalization contract.

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?

Provides useful operating context (must pass the saved plan revision and a stable operationId for safe retries) and notes there is no model call or credit charge. However, it never names an alternative tool or states when to prefer this over studio_film_scenes_write or studio_film_edit_line, so usage is implied rather than directed.

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