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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds one piece of real context beyond that — the plan-based history window — but says nothing about response shape, ordering, gaps for non-trading days, or pagination/volume limits for full-history requests.

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 short sentences, front-loaded with the resource, with the plan caveat second. No filler. It is written as a noun phrase rather than an imperative, which makes it slightly less directive than it could be, but nothing is wasted.

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?

All five parameters are fully documented in the schema and there is no output schema to explain, so the description's remaining burden is scope plus constraints — both of which it covers, including the future-date clamp being handled in the schema. The one missing piece is disambiguation from the several sibling analysis/rate tools.

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%, and the schema already spells out defaults, ISO 4217 format, and the interval bucketing rules in detail. The description's only parameter-relevant claim ('a single currency', 'daily rate time series') restates what the schema's currency and interval descriptions already say, adding no new semantics — baseline 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 names the concrete resource ('a single currency's daily rate time series over a date range'), which is specific enough for an agent to know exactly what data comes back. It does not, however, distinguish this from the sibling 'analyze_history' or 'get_rates', so the agent must infer the boundary from the names alone.

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 tier restriction ('Free: last 30 days; Starter and above: full history') is genuinely useful usage guidance because it tells the agent when calls will return truncated data. But there is no statement of when to prefer this tool over analyze_history or get_rates, and no exclusions or prerequisites beyond the plan limit.

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