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

Annotations already establish that this is a read-only, non-open-world operation. The description adds meaningful behavioral context beyond annotations by disclosing the $0.003 USDC x402 cost and the 366-day maximum range.

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 a single front-loaded sentence with no wasted wording. It packs the resource, constraints, output summary, and cost into a compact form.

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 read-only rate-series tool with a fully described schema and annotations covering safety, the description is largely complete. It discloses the output statistics and payment cost, though it could be slightly more explicit about base/symbol ordering or error conditions.

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 coverage is 100%, so the schema already documents all four parameters and their date formats. The description adds the useful max 366-day constraint on start and end, but does not clarify the distinction between base and symbol beyond restating them together.

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 a specific resource (daily reference rate series), the pair of currencies, the date interval, and the aggregate outputs. It implicitly distinguishes the tool from rates_latest and convert by emphasizing a ranged daily series, though it does not explicitly call out when to use the sibling tools instead.

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?

Usage is implied by the stated range and max 366-day limit, but there are no explicit when-to-use or when-not-to-use instructions and no named alternatives. An agent can infer that this is for ranged daily series, but must compare against siblings on its own.

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