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

Annotations cover read-only and open-world behavior, and the description adds genuinely useful context beyond them: the paid nature of the call ($0.005 USDC via x402 on Base) and the exact rate components returned. It stops short of stating cost/rate-limit failure behavior, but the payment disclosure is material.

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?

One front-loaded sentence covering the core purpose and return content, with a short payment clause appended. No filler, though the payment sentence sits slightly apart from the main statement.

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 read-only tool with no output schema, the description usefully states what comes back (rates plus official date and source). Remaining gaps are input-syntax details (date/currency format, date default) rather than missing behavioral essentials.

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 0%, so the description carries the burden; 'for one currency on a date' does map ccy and date to their meaning. However it gives no format for either (ISO 4217? ISO date?), and does not explain what happens when the optional date is omitted, so the compensation is only partial.

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?

Names a specific resource and scope ('Won exchange rate for one currency on a date') and enumerates the returned rate types (KEXIM deal basis, TTB, TTS) plus the official date and source. Clear enough to distinguish from most siblings, but it never acknowledges kr_rates_query, which is the obvious overlapping tool.

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 single-currency, single-date framing implies when the tool applies, but there is no explicit when-to-use, when-not-to-use, or routing to the near-neighbor kr_rates_query. An agent must infer the boundary itself.

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