list_currencies

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

With no annotations present, the description carries the full burden and does so well: it discloses the exact return shape, includes a count field, states the currency universe (160+ ISO 4217 fiat), notes the exclusion of crypto, and flags that it is cheap to call. This gives the agent a clear behavioral model for invoking it safely.

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 compact, front-loaded with the most important usage instruction ('Call this BEFORE other tools'), and every sentence earns its keep: when to use, return shape, coverage, exclusion, and downstream value. No filler.

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 zero-parameter read-only tool with no output schema, the description fully compensates by defining the response structure and enumerating coverage. It also answers likely agent questions about validity, symbols, quantity, and relationship to sibling rate tools. Nothing needed for correct invocation 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?

The tool has zero parameters, so the description cannot add meaning beyond the schema; baseline 4 applies. It still usefully explains what the returned codes represent and how they relate to other tools, but there is no parameter-specific detail needed.

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 names the specific resource (supported currencies and their metadata) and the action (list/validate), and clearly differentiates itself from the rate-focused sibling tools. It also adds scope details like '160+ ISO 4217 fiat currencies' and explicitly excludes cryptocurrencies.

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 gives explicit when-to-use triggers ('before other tools... when unsure whether a currency code is supported'), user-phrase examples, and tells the agent to use it to prevent downstream errors in get_exchange_rate, get_rates, and get_historical_rates. It also states what it does NOT cover (cryptocurrencies), leaving no ambiguity about its role versus siblings.

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