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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds valuable behavioral detail beyond annotations: the sort order, the exact fields returned, the limit/totalOffers semantics, and the fallback-to-search behavior. This gives the agent a clear picture of what will happen when invoked.

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 three sentences, each earning its place: the first states the purpose and sort order, the second lists output fields, and the third explains the limit and fallback behavior. It is front-loaded with the core purpose and contains no redundant text.

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?

Given the tool has no output schema, the description adequately explains the return values, ordering, included fields, and fallback behavior. The parameter semantics are covered by the schema and enriched by the description, and the annotations handle safety expectations. Nothing essential is missing for an agent to invoke 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?

Schema coverage is 100%, so the baseline is 3. The description adds meaning beyond the schema by explaining that `model` can be a canonical slug or partial name and triggers a fallback search, and that `limit` determines the number of cheapest offers returned alongside totalOffers. This enriches the parameter understanding.

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 action ('compare model prices') and resource ('every gateway offering one canonical model') and clearly specifies the output: cheapest input price first, with context length, cached-input price, isFree, referral link, last synced, and totalOffers. It also distinguishes itself by describing a fallback to search when the exact slug is unknown, which clarifies its unique role among siblings.

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 implies usage: call this tool to get the cheapest offers for a canonical model, and it notes that a partial slug triggers a search. However, it does not explicitly state when to prefer this tool over siblings like search_models, estimate_cost, or list_gateways, nor does it provide explicit exclusions.

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