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

With readOnlyHint: true already declaring this a safe read, the description adds the upstream source (open.er-api.com), which hints at freshness and reliability. However, it does not disclose update frequency, rate-limit behavior, or which currencies are covered – context that matters for a rate-lookup tool.

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?

A single front-loaded sentence with no filler, correctly scoping the tool before the source citation. It is perhaps terser than ideal, but every element earns its place.

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 simple one-parameter read tool with annotations and full schema coverage, the description is adequate but incomplete: it never mentions the return shape (which currencies are returned, whether a rates map is provided) even though no output schema exists to fill that gap.

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% and the single parameter (base) already documents the default (USD) and example values (USD, CNY, EUR) in the schema itself. The description adds nothing on top of that, so the baseline of 3 applies.

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?

States a specific verb (query) and resource (real-time exchange rates) with the scope (major currencies vs a base currency) and even the data source (open.er-api.com). This differentiates it from the sibling currency_convert, which clearly performs conversions rather than listing rates.

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 only implied by the word '实时汇率' – the agent can infer this is a rate lookup rather than a conversion, but there is no explicit when-to-use vs currency_convert guidance, no mention of whether rates are cached, and no stated limits.

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