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

With no annotations, the description carries the full burden and does well: it discloses update cadence (once per working day), that the response states the effective day, the ~30 currency universe, and a paid x402 cost of $0.005 USDC on Base. Missing only error/failure behavior and any rate-limit or caching notes.

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?

Three tight sentences, front-loaded with resource and scope, then cadence, then payment cost. Nothing is redundant.

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 zero-required-param read tool with no output schema, the description covers cadence, effective-date reporting, currency coverage, and payment cost — everything needed to invoke it. A brief note on returned structure or the convert alternative would make it complete.

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 all three parameters are already documented, giving a baseline of 3. The description reinforces base-currency and date semantics but adds no format or interaction detail beyond the 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 (European Central Bank daily reference rates) and scope (about 30 major currencies, any base, latest or historical). An agent can tell this returns rate data rather than computing a conversion, but it never names fx_ecb_convert, so the sibling boundary must be inferred.

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?

"Latest or for a past date" gives implicit selection guidance, but there is no explicit when-to-use statement and no routing to fx_ecb_convert for actual currency conversion. The usage context is inferable rather than stated.

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