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

Annotations already declare readOnly, idempotent, non-destructive, closed-world; the description complements them by disclosing the actual payload contents (labels, product groups, APY/APR semantics, state codes). No permissions or rate-limit caveats are mentioned, but none are plausibly needed for a static lookup.

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 sentences, zero filler, and the payoff (what a rate key carries) is front-loaded ahead of the secondary state-code behavior. Nothing could be removed without losing information.

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?

With no output schema and no parameters, the description carries the full burden of conveying return values, and it does so concretely: key, label, product group, APY/APR flag, plus state codes. An agent can call this and interpret the result without further information.

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 tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description correctly avoids inventing arguments.

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 (lists) and resource (rate keys, U.S. state codes) and enumerates exactly what each entry contains: label, product group, and APY vs APR. It also names the sibling consumers (get_best_rates, get_average_rates), so it is unmistakable against the other 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?

The phrase 'accepted by get_best_rates and get_average_rates' tells the agent this is the discovery step to run before those tools, which is a clear usage context. It stops short of an explicit instruction ('call this first') or exclusions, so it lands at 4 rather than 5.

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