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

Goes well beyond the annotations: discloses the data source (European Central Bank), the pricing model ($0.01/call via x402 USDC or card key, first 25 free, failed calls free), and warns that repeats are not free despite being a read. It also clarifies the read/compute-only semantics and confirms no side effects, consistent with readOnlyHint=true.

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-loads what the tool does and the currency coverage, then usage and pricing. Dense but nearly every sentence carries information; the pricing/charging sentence is somewhat packed but still earns its place as cost-relevant behavior.

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 still explains returns (rates, converted amounts, applicable date), data source, currency set, parameter behavior, and cost. An agent has everything needed to call it and interpret results.

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 the baseline is 3; the description adds a concrete example (from=USD) and clarifies the base-vs-target relationship and that targets default to all currencies. It adds modest value over the already-complete schema.

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 resource (ECB foreign exchange rates for ~30 major currencies) and the inputs/outputs (base currency, optional targets and amount, returns rates, converted amounts, rate date). The named currency examples and conversion output make it clearly distinguishable from the crypto-oriented siblings like price_token or btc_price.

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?

Explicitly lists when to use it: currency conversion, invoice and price calculations, and reporting in another currency, plus a worked example (from=USD). It does not explicitly name an alternative or exclusion case, so it stops 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.