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

Goes well beyond the annotations: discloses that rates come from the ECB and are informational only, not for transactions; specifies pricing ($0.002 USDC per call over x402), that failed calls cost nothing, and that the first 3 calls/day are free without a wallet. This is exactly the rate-limit and cost context an agent needs.

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?

Front-loaded with the core purpose, followed by source/caveat and then payment mechanics. Three short paragraphs, each earning its place; slight verbosity in the pricing detail but nothing wasteful.

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 conversion tool with no output schema, the description covers source, coverage, date range, and payment flow. It does not describe the response shape (e.g., rate vs converted amount), a minor gap given the output schema is absent.

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 already 80%, so the schema documents from/to/date/amount. The description adds meaningful semantics for `payment` (omit it to receive a quote, sign and call again) and corroborates the 90-day date window, going beyond the baseline.

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 (convert) and resource (currencies) with clear scope: ECB reference rates covering 30 currencies for the latest business day or any day in the last 90. An agent can immediately distinguish this from siblings like token_price or wallet_balance.

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?

Gives clear usage context (currency conversion using official ECB rates) and an operational hint: call without `payment` to get a quote first. It does not explicitly name an alternative sibling or state when-not-to-use, so it falls short of a 5.

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