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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description earns credit for disclosing provenance — these are the historical rates GWIX actually applied to USD pay reporting, not live market rates — and for noting the call is free; it does not cover pagination or result volume.

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 usage guidance is front-loaded, but the description repeats itself: 'Returns units per USD for each currency and period' and 'Exchange rates GWIX used (units per USD) per currency and period' say the same thing. The trailing 'Free.' fragment is also abrupt rather than integrated.

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 no output schema and no required parameters, the description supplies the essential missing piece by explaining what a result row means (units per USD per currency per period). It leaves unresolved what happens when neither currency nor country is supplied, which matters given zero required parameters.

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 100%, so all five parameters are already documented with examples and the enum for interval. The description restates the same information (currency codes or countries, an interval, an optional period range) without adding format details beyond the schema, so the baseline 3 applies.

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 states a specific verb and resource — retrieving the exchange rates GWIX applied when reporting pay in USD — plus the return unit ('units per USD for each currency and period'). It also implicitly separates this from get_pay by framing it as the tool for converting or explaining non-USD pay.

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?

'Use to convert or explain non-USD pay' gives a clear trigger condition, and 'Free' signals there is no cost barrier to calling it. It does not name an alternative tool or state when not to use it, so it stops short of full routing guidance.

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