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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world behavior. The description adds meaningful context beyond that: prices are recorded USD text-token rates, and expired or unreviewed rates are informational only, which helps the agent interpret data freshness and reliability.

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?

The description is tightly structured: usage context and prerequisite first, parameter guidance second, data caveat third, and alternative tool last. Every sentence adds distinct value with no redundant or filler content.

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 simple single-parameter lookup tool with full schema coverage, annotations, and an output schema, the description covers usage context, the alternative tool, and important data-freshness limitations. Nothing an agent needs to select or invoke the tool correctly is missing.

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 100%, and the schema's model_id description already explains that it must be the exact pricing-offer ID returned by list_models or find_cheapest_models. The tool description reinforces this with 'Supply the returned model_id' but adds no semantic detail beyond the schema, so the baseline 3 is appropriate.

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+resource: retrieving the rates, tariff identity, sources, and freshness of one exact offer. It explicitly distinguishes itself from calculate_cost (workload estimate) and implies its relationship to list_models, so an agent can tell it apart from siblings without opening schemas.

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?

It says to use this tool after list_models and when an exact offer is needed without calculating a workload. It names calculate_cost as the alternative for workload estimates, providing explicit when-to-use and alternative guidance.

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