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

Annotations already declare readOnly/idempotent/non-destructive/non-open-world, so safety is covered. The description adds value beyond them by disclosing cost profile ('Deterministic, free, no charge') and the shape of the output (four named delivery energies plus the directionality rule for seconds vs. energy).

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?

Purpose is front-loaded in the first sentence and the rest is mostly load-bearing. 'Fewer seconds is faster... more seconds is slower' and 'Deterministic, free, no charge' carry slight redundancy but earn their place as disambiguation/cost signals.

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?

No output schema exists, so the description must describe the return shape — and it does, enumerating the four energy tiers and the seconds-vs-energy relationship. Combined with usage and cost info, an agent has everything needed to call and interpret it.

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% with only two optional, mutually-substitutable params, so the baseline is 3. The description reinforces the either/or semantics ('the spoken text (or a word_count)') and the counting behavior, adding marginal clarity, though it never addresses the zero-required-params case of supplying neither.

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 precise verb+resource: computes how many seconds a spoken line should occupy. It clearly distinguishes itself from the generation siblings (generate_speech, talking_avatar_video) by being a pure estimation/advice tool, not a renderer.

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?

Explicitly states when to use it: 'whenever a user asks how long to make a clip for their narration or dialogue, or which duration to pick for a given energy.' That is a concrete trigger condition an agent can match against intent.

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