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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds important behavioral context beyond them: the $0.001 USDC x402 payment cost, ECB reference-rate source, support for historical dates, and returned fields ('rate, result and as_of date'). There is no contradiction with the annotations.

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?

The description is one compact, front-loaded sentence group with zero filler. It moves efficiently from purpose to example to historical-date support to return values and payment cost.

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?

Given four parameters, no output schema, and existing read-only annotations, the description is complete enough for correct invocation. It covers the input example, data source, historical date option, return fields, and payment requirement.

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 description coverage is 100%, so the baseline is 3. The description adds useful semantic context with the example '100 USD to JPY' and the note that a past date can be used, clarifying how 'from', 'to', 'amount', and 'date' work beyond the minimal schema descriptions.

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 uses a specific verb and resource: 'Currency converter: convert an amount between any two of ~30 currencies.' It includes a concrete example ('100 USD to JPY') and clearly distinguishes conversion behavior from the sibling rates tools by focusing on converting an amount rather than returning raw rates.

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 clearly states the primary use case: converting an amount at the latest ECB reference rate or as of a past date. The sibling tools imply alternatives for raw rates, but the description does not explicitly name rates_latest, rates_historical, or rates_timeseries or state when to prefer them over convert.

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