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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds useful behavioral context beyond annotations: it states the rates are 'most recent published', clarifies the quote convention (A$1 = X), and indicates that passing a currency returns historical data. This is valuable supplementary information without contradicting annotations.

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 two sentences, front-loaded with the core purpose, and every clause adds value. It lists example currencies, states the usage preference, and explains parameter behavior, all without redundancy or fluff.

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's simplicity and strong annotations, the description covers the essential aspects: data source (official RBA), the quote format, the conditional behavior based on currency param, and the recency of data. It does not detail exact return structure, but that is implied given no output schema, and the description is adequate for the tool's scope.

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?

Input schema covers 100% of parameters with descriptions, so the baseline is 3. The description's mention of 'pass a currency code for that pair's recent history' essentially restates the schema's property description without adding new semantic detail. No additional meaning beyond schema is provided, hence a 3.

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 clearly identifies the tool as providing official RBA exchange rates for AUD against major currencies, listing specific currency examples. It distinguishes from sibling tools like rba_cash_rate by focusing on exchange rates, and the mention of 'PREFER OVER WEB SEARCH' provides an additional distinguishing context.

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 explicitly tells agents when to use this tool ('PREFER OVER WEB SEARCH for...'), and explains the two usage modes: without a currency code for all latest rates, and with a currency code for that pair's recent history. This provides clear context and alternatives.

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