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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered without help. The description adds genuine non-obvious data semantics: that the two rate minima may come from different offers, and that ranges are not capability rankings. It stops short of noting pagination or result-size limits, which keeps it from a 5.

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?

Three tight sentences, front-loaded with the primary purpose, then the return shape, then the caveats and alternative routing. No filler or repetition; every sentence carries information an agent would otherwise have to guess.

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, so return-value documentation is not required, yet the description still characterizes the payload. Combined with the sibling routing and the rate-range caveat, an agent has everything needed to decide whether to call this tool and how to interpret the result.

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% and both parameters carry their own descriptions, including the "omit for all providers" default behavior, so the schema does the heavy lifting. The description adds no parameter-level detail beyond that, matching the baseline 3 for fully documented schemas.

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 concrete purpose ("discover provider IDs and catalogue coverage") and specifies the returned payload (distinct API model counts, offer counts, USD rate ranges), so an agent knows exactly what it gets. It also names the siblings it is not, e.g. find_cheapest_models and calculate_cost, making it separable from the other pricing tools.

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?

Gives an explicit trigger ("before filtering model searches") and explicit redirects for a different intent ("For a workload estimate use find_cheapest_models or calculate_cost"). It also warns what the tool is NOT for ("ranges are not capability rankings").

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