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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description still adds useful context: "Public, no key needed" (auth requirement) and the deliberate fail-clearly-rather-than-silently behavior for unsupported codes. It stops short of describing the shape of the returned records, which matters since no output schema exists.

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?

Three short sentences, front-loaded with what it is, then when to use it, then the auth note. No filler or restated title.

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 zero-param reference lookup this covers purpose, usage, auth, and failure behavior. The only gap is that, with no output schema, the exact fields returned (code/name/symbol per entry) are implied rather than stated.

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?

The tool takes zero parameters, so the schema baseline applies and there is no parameter meaning to add. The description does not need to compensate for anything here.

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 full list of supported ISO 4217 currencies" names a specific resource and scope, and the mention of codes/names/symbols tells the agent exactly what data is inside. It is unambiguously distinct from numeric siblings such as convert, get_rates, or analyze_* which operate on data rather than enumerating reference values.

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?

Two concrete use cases are given: resolving a name/symbol to a code, and validating support before use. That is clear when-to-use context, but there is no explicit when-not or named alternative (e.g., no instruction that convert assumes an already-known code), so it falls short of the top band.

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