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

Annotations cover the safety profile (readOnly, non-destructive, openWorld), and the description adds genuinely useful context beyond them: the rate source (ECB via Frankfurter), that rates are live, and a specific cost ($0.003 USDC on Base via x402). It does not mention freshness/latency or rate limits, keeping it short of a 5.

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?

A single front-loaded sentence packs purpose, source, conversion capability, and price with no filler. Dense but every clause earns its place.

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, the description never sketches the return shape (e.g., a rate per target vs a conversion result), which an agent would benefit from. It otherwise covers purpose, source, and pricing adequately for a simple 3-param lookup.

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% with clear per-parameter descriptions, so the schema already carries the semantics. The description reinforces the multi-target and optional amount-conversion behavior but adds no syntax or format detail beyond what the schema provides; 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?

States a specific verb+resource ('FX exchange rate + convert'), the scope (one base to one or more targets, optional amount), and the data source (ECB reference rates via Frankfurter). This distinguishes it from the crypto_pricing siblings without needing to open a schema.

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 description implies its use case (live exchange rates and conversion) but never states when to reach for it versus alternatives such as crypto_price, nor any exclusions. Usage is inferable from the scope but not spelled out.

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