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

Beyond the readOnly/non-destructive annotations, it discloses that the call costs nothing, that no job is started, that an account plan tier is required, and that 3D pricing rounds up per started minute. Those are exactly the side-effect, entitlement, and billing rules an agent cannot infer from annotations.

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?

Three short sentences, front-loaded with the return value, then cost/safety, then prerequisites, then the rounding caveat. Every sentence carries information, though the phrasing "the answer's seconds is the longest it may run for" is slightly awkward.

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 does the necessary work of naming what comes back (credit cost and balance) and covers prerequisites and pricing behavior. It leaves only minor gaps, such as whether the quoted price can change before the actual render is requested.

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%, so the baseline is 3, but the description adds real meaning: the returned "seconds" for 3D is the maximum runtime for that price, illustrated by "15 s asked = up to 60 s." That explains the rounding semantics of the seconds parameter in a way the schema does not.

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?

The description states a specific verb and result: it returns the credit cost for a video of a given kind and length plus the account balance. That makes it unambiguous against siblings like make_video (which would actually produce a video) and get_video/list_my_videos (which fetch existing ones).

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?

"Free, and nothing starts" plus the plan requirement tells the agent this is a safe preview step, implicitly the thing to call before make_video. It never names make_video explicitly or states when-not to use it, so it stops short of explicit routing.

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