view actual generation costs

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

Beyond the readOnly/idempotent/non-destructive annotations, it discloses non-obvious response behavior: totalCostUsd is null unless availability is complete, knownSubtotalUsd must be presented as partial, retryAfterSeconds requires a re-read, and excludedCosts (tax, subscription fees, external charges) are not counted. It also states error behavior for unknown or inaccessible ids, which annotations do not cover.

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 and exclusions are front-loaded, and the later sentences are dense but each carries operational content (nullability, retry loop, presentation rules, error case). It is slightly overlong for a one-parameter read tool, and the output-presentation directives could be tightened, but there is little pure filler.

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?

An output schema exists, yet the description still supplies the semantic contract the schema cannot express: when totals are null, how to poll, and which costs are excluded. Combined with recovery guidance for a missing id, an agent has everything needed to call and interpret 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?

The single parameter is fully documented in the schema (100% coverage), so the schema carries the format burden. The description still adds sourcing guidance absent from the schema — where to obtain the id and what to do when multiple candidates match.

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 first sentence gives a specific verb and resource (read the recorded cost of one past generation) and names the exact component breakdown (lipsync, dubbing, speech_synthesis). It is immediately distinguishable from generations_estimate-cost and account_get-usage, which are named 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?

The description states when to use it (answering what a generation actually cost) and when not to (pre-generation pricing, remaining credits), and explicitly forbids substituting an estimate or triggering a paid generation. It also covers the prerequisite path: look up generationId via generations_list or projects_list-generations and ask the user when several match.

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