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

Annotations already declare idempotentHint, destructiveHint, openWorldHint and readOnlyHint, so the bar is lower; the description still adds real value by naming the return value, the optimistic-concurrency contract via expectedRevision, the retry-reconciliation semantics, and the fact that no model call or credit is consumed. It omits what happens on a stale revision (conflict/error behavior) and where in the scene the line lands.

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 purpose and return value before the concurrency/retry mechanics and the cost note. Every clause carries information; nothing is padding.

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?

With an output schema present and full parameter coverage, the description only needs to carry the behavioral contract, which it does: idempotent retry reconciliation, revision-based concurrency, and no credit charge. An agent has everything required to call this correctly.

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 the schema already documents all five parameters in detail. The description restates expectedRevision and operationId semantics rather than adding new meaning, so baseline 3 is appropriate.

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 ('Add one finished dialogue line to a scene') plus the return value ('return its lineId'), which inherently separates it from studio_film_edit_line and studio_film_remove_line. The closing claim 'No model call or credit charge' further distinguishes it from generation siblings such as studio_generation_* or studio_media_*.

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 clear operating context: it needs expectedRevision (the current saved plan revision) and a stable operationId, and it explains that identical operationId/input retries reconcile to the same edit, which tells the agent how to behave on retry. It stops short of explicit exclusions or pointing to studio_film_edit_line for changes to an existing line.

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