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

Annotations already provide readOnlyHint=true and destructiveHint=false, so description adds value by noting 'Updated daily on free tier' and 'Returns all rates in one call', which informs about update frequency and bulk retrieval behavior beyond what annotations convey.

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 concise sentences that front-load the core purpose, with no redundant or extraneous words. Every sentence provides essential 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 single-optional-parameter tool with comprehensive annotations and an output schema, the description fully communicates scope, availability, and behavior. Leaves no significant gaps for agent decision-making.

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 description covers the 'base' parameter fully (100% coverage), and the tool description does not add additional interpretation or constraints beyond what the schema already provides.

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?

Clearly states it provides latest exchange rates for 160+ currencies against any base currency. Distinguishes from sibling currency.exchange.convert by noting 'Returns all rates in one call' – implying this is for bulk rates, not conversion.

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?

Provides clear context: 'Latest exchange rates for 160+ currencies against any base currency' and 'Returns all rates in one call'. Implies use for comprehensive rate retrieval, but no explicit exclusions or comparisons with alternative tools like currency.exchange.convert.

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