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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is fully covered. The description adds nothing further: no note on lookup-miss behavior, no indication of what a nonexistent currency_id returns. It does not contradict the annotations, but it contributes no behavioral context of its own.

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 words is technically compact, but this is under-specification rather than conciseness. There is no front-loaded statement of action or scope an agent could act on.

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 and rich annotations relieve some burden, so return values and safety need not be described. Still, for a callable lookup tool with a required identifier parameter, the description leaves the action, the parameter's meaning, and the sibling relationship 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?

The tool has one required parameter, currency_id, at 0% schema description coverage; the description never mentions it. The schema's own examples (BTC, USD) carry the only format signal available, and the two-word description does not compensate for the coverage gap.

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?

"Single currency." is a noun fragment, not a verb+resource statement. The word "single" hints at a per-currency lookup as opposed to the sibling coinbase_exchange_currencies list, but an agent gets no explicit statement of what the tool returns or does.

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?

There is no when-to-use guidance, no mention of the plural list sibling as the alternative, and no statement of any prerequisite such as needing a valid currency identifier. Usage must be inferred entirely from the name.

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