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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds real context beyond that: the list is 'live' (dynamic, not a frozen constant) and its contents are ISO 4217 fiat plus metal codes, which tells the agent what kind of values to expect.

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?

A single front-loaded sentence that names the resource first and its scope second, with no filler. Every clause carries 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?

For a simple read-only catalog tool with an output schema covering return values and annotations covering safety, the description supplies what is needed: what the list contains and what it is for. Only the pagination/limit behavior is left entirely to the schema, a minor gap.

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 67% (query and cursor are documented, limit is not), so the schema carries most of the parameter burden. The description adds no syntax or filtering detail for limit/query/cursor, and its reference to `currency`/`base` parameters concerns other tools rather than this tool's inputs — 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?

States a specific verb and resource (list of supported currency codes) and defines the resource precisely as the set of values accepted by any `currency`/`base` parameter, which cleanly separates it from the pricing siblings (get_spot_prices, get_goldback_rate). An agent can tell this is a catalog lookup, not a rate fetch, without opening the schema.

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?

Framing the list as 'every `currency`/`base` parameter accepts' tells the agent exactly when to reach for it — to validate or discover valid code values before a pricing call. It stops short of an explicit when-not or a named alternative, but the intended usage is unambiguous.

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