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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds information annotations cannot express: the call is free and reserves no credits. It still doesn't say whether validation failures surface as errors or as a field in the response.

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 tight sentences with the cost outcome front-loaded and the no-side-effect guarantee immediately after. Zero waste.

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 4-param, no-output-schema tool, the description conveys the primary return (credit cost) but leaves the shape of validation results unstated and says nothing about accepted resolution/duration ranges. Adequate but with clear gaps an agent would hit on first call.

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 only 25% — duration, resolution (no enum), and audio have no descriptions anywhere. The description mentions no parameters at all, so it does not compensate for the coverage gap; it only hints that settings will be validated.

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 specific verbs and outcome: 'Validate settings and calculate the exact credit cost.' The clause 'does not generate or reserve credits' functionally separates it from generate_video without naming the sibling explicitly.

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?

Implies the pre-generation estimation use case via 'Free; does not generate or reserve credits,' but never says 'call this before generate_video' or names any alternative. An agent must infer the workflow placement.

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