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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is fully covered. The description adds value by enumerating the return fields (name, symbol, decimal places), which matters since there is no output schema, but it says nothing about behavior for an unknown or invalid code.

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 tight sentences: the action first, the return shape second. No filler, no redundancy, and the reader gets the essential facts immediately.

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 one-parameter read tool with complete annotations and no output schema, the description covers what it does, what it takes, and what it returns. Only the error behavior for a missing currency code is unaddressed.

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 the single 'id' parameter is already fully documented with matching examples ('nzd', 'usd', 'gbp'). The description repeats the same examples without adding format rules such as case sensitivity, so baseline 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 and resource ('Gets a specific currency by its code') and even previews the return fields. It implicitly contrasts with list_currencies via 'a specific currency', but never names that sibling, so differentiation is inferred rather than stated.

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 use case (look up one currency when you already have its code) is implied by 'by its code', but there is no explicit when-to-use, when-not, or pointer to list_currencies for browsing all codes. An agent must infer the routing.

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