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

Goes well beyond readOnlyHint/openWorldHint by disclosing the pricing model ($0.002 USDC per successful call, x402 on Base/Solana/Arc) and that failed calls are not charged — a real cost/risk signal for the agent. It also states result ordering (latest months first) and that values are as published.

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?

Four tight clauses: what it is, format/ordering, scope caveat, price. The critical identifying information is front-loaded and nothing is 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?

With an output schema present, the description needn't explain return structure; it covers source, unit, ordering, coverage caveat and cost. Nothing an agent needs to call this correctly 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?

Schema coverage is 100%, so baseline is 3, but the description adds real meaning beyond the schema: 'for one country' clarifies that country selects a single series, and 'latest months first' explains how the months parameter is applied.

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?

Names the exact resource (BIS nominal broad effective exchange rate), the entity scope (one country), the unit/format (monthly index values, base 2020 = 100) and the source API. It also disambiguates from bilateral rates, so an agent can tell what family of data this is 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?

The 'not a bilateral rate' and 'broad basket of 64 economies' notes give context for selection, but there is no explicit when-to-use/when-not or any named alternative among the many sibling tools. Usage is implied rather than routed.

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