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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered structurally. The description adds genuinely useful behavioral context beyond that: 5 prepaid credits, production billing required, and that prices are caller-supplied rather than looked up. It does not say what happens when credits are insufficient or how the estimate is computed (no rounding/currency assumptions).

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 short sentences, front-loaded with the core action and followed by the billing constraint; no filler. Slightly dense phrasing ("caller-supplied per-tool quantities and USD prices") but efficient.

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 single-parameter estimator with no output schema, the description covers the economic model and the paid-access constraint, which the agent needs before calling. It is incomplete on the shape of array elements and on the exact credit-charging semantics, which matter for a metered tool.

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?

One parameter (items) with 0% schema description coverage and an untyped array element, so the description must compensate. It partially does by stating each entry carries a per-tool quantity and a USD price, but gives no field names, units, or format for those entries.

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 ("Estimate costs") plus the input basis (caller-supplied per-tool quantities and USD prices), which is more than a restatement of the name. It does not distinguish itself from plausible siblings like privi_pro_model_cost_estimate or privi_token_cost, leaving the agent to infer the boundary.

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?

No when-to-use or when-not-to-use guidance is given relative to the other cost-estimation tools. The only contextual note is a billing prerequisite (paid only, 5 prepaid credits), which tells the agent about cost, not about tool selection.

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