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

Annotations declare readOnlyHint=true and the description is consistent with a pure read. Beyond annotations it adds genuinely useful context: a per-call price ($0.05), the data source (ECB reference rate), and the shape of the response (converted figure, rate used, rate date). It does not cover error behavior for unsupported currency codes, which keeps it from a 5.

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 sentence that front-loads the cost, then the action, then the return shape. No filler; every clause carries information an agent needs before calling.

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 no output schema, the description correctly takes on the burden of describing return values (figure, rate, date) and also discloses pricing and the rate source. Only edge-case behavior — unsupported currency codes, rounding — is left unstated.

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 all three parameters already carry descriptions including the USD/IDR defaults, making 3 the baseline. The description adds only the note that IDR is supported as a target, which is marginally useful for this Indonesia-focused toolset but does not add syntax or format detail beyond the schema.

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 and resource ('convert an amount between currencies') plus the rate source (ECB reference rate) and the return contents. It implicitly distinguishes itself from the rate-listing sibling indonesia_fx, but never names that sibling, so the differentiation is inferential rather than explicit.

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 verb — use this when you need an actual converted figure rather than raw rates — but there is no explicit when-to-use/when-not guidance and no mention of the alternative indonesia_fx tool. An agent can infer the context but is given no routing rule.

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