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

There are no annotations, so the description carries the entire behavioral burden, and it discloses almost nothing: it doesn't say whether the rate is live or cached, is silent on the subscription/access_token requirement that the schema hints at, and says nothing about reversibility or response shape. Only the "PRO." marker hints at a paid tier.

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 short sentences, front-loaded with the action and the scoping constraint. Nothing is redundant or padded.

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 four parameters, 25% schema coverage, no annotations and no output schema, the description should say more than it does – the auth path, the direction of conversion, and what the tool returns (converted amount, rate used) are all absent. An agent can guess the call shape but not the contract.

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 only 25% – `from` and `to` have no descriptions at all – so the description must compensate. It does add the meaningful constraint that one of the two currencies must be JPY, but it leaves ambiguous whether `from` or `to` must be the yen side, gives no currency-code format, and doesn't say whether `access_token` is mandatory.

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?

"Convert an amount between JPY and another currency" states a specific verb (convert) and resource (monetary amount) plus a scope constraint (one leg must be JPY). It is clear on its own, but it never names or distinguishes itself from the siblings fx_rate and fx_table, so an agent can't route between the three from this text alone.

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 only implied: the JPY constraint tells the agent the tool applies to yen pairs, but there is no statement of when to prefer it over fx_rate (single rate lookup) or fx_table (bulk rates). No explicit when-not cases and no named alternatives.

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