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

Annotations already declare readOnly, openWorld, and idempotent, so the safety profile is covered. The description adds genuinely useful context beyond them: rates are live market rates refreshed hourly, and results are rendered as an interactive card, which tells the agent about freshness and output shape.

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 sentences, zero filler. The core action and scope come first, format guidance second, and the coverage/freshness detail last.

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?

An output schema exists, so return values need no explanation, and the description covers action, input format, scope, and freshness. Only omission is any note on the maxItems limit or behavior when an unsupported code is passed.

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 are already documented with examples. The description reinforces the ISO 4217 format, which the schema examples also convey, and adds nothing about the array cap of 12 or the amount default. Baseline 3 is appropriate.

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 states a specific verb and resource ('Convert an amount from one currency into one or more others'), the conversion basis (live market rates), and the presentation form (interactive card). An agent knows exactly what the tool produces without opening the schema.

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?

It tells the agent how to invoke the tool (ISO 4217 codes, with examples) and the breadth of coverage (166 currencies, hourly refresh), but there are no sibling tools so no when-not-to-use guidance is needed or given. Clear context, no exclusions.

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