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

Annotations already declare readOnlyHint/idempotent/non-destructive, and the description reinforces this with 'Does not spend' — the consequence that matters to a caller. It also discloses a non-obvious behavioral caveat: the returned figure is an estimate that diverges from the binding price stored on the video's button, which is not derivable from any structured field.

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 purpose and the 'does not spend' caveat before the longer chain reference. The second sentence is dense with tool-name arrows and could be tightened, but every clause carries real routing 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?

With no output schema, the description still conveys what comes back (a rough price figure) and how much to trust it. Combined with the safety annotations and the pipeline guidance, an agent has enough to call it correctly; only the tier nuance is unaddressed.

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 75% and already documents tier, brand_id, and user_goal, so the baseline is 3. The description adds meaning for duration_seconds (the estimate is driven by film length) but never mentions the tier parameter, even though b_roll/standard/premium clearly affect the quote — a meaningful semantic gap left entirely to the schema.

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 ('Rough price of a film from its length in seconds') plus the exact framing (budgeting estimate, not a commitment). It explicitly separates itself from the real price source (get_studio_video `button.credits`) and from the film-making siblings, so an agent can distinguish it without opening the 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 the when ('for budgeting before you start'), the when-not ('Does not spend'; this number is not the agreed price), and the correct downstream path (create_motion_project → studio_video_message → make_studio_video). Nothing about tool selection is left to inference.

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