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

Annotations already establish readOnly/idempotent/openWorld, yet the description adds substantial context they can't convey: it is a paid x402 tool at 0.002 USDC per call, an unpaid call returns a payment-required result with structuredContent, the caller must sign an accepts entry and retry with PaymentPayload, source failures are not charged, and settlement appears in result._meta. This is exactly the beyond-annotation disclosure the dimension rewards.

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 purpose and selection rule are front-loaded in the first sentence, followed by the payment mechanics. It is dense and mostly earns its length, though the x402 retry/settlement explanation makes it longer than a typical read tool needs.

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 one-parameter read tool with no output schema, the description covers everything an agent needs: what is returned (JSON text), the rate fields, the payment requirement and failure modes, and where settlement lands. Nothing essential is missing.

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% and the single parameter already has a full enum with a default, so the schema does the heavy lifting. The description adds only marginal value by clarifying the {} for-all vs {casa} for-one usage and the bolsa/MEP naming correspondence; baseline 3 is appropriate.

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 names a specific resource (current Argentine dollar quotes in ARS per USD) and enumerates every rate variant (oficial, blue, bolsa/MEP, CCL, mayorista, cripto, tarjeta). That level of specificity clearly separates it from generic siblings like fx_rate and from the other ar_* lookup tools.

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?

"Send {} for all or {casa} for one" gives explicit invocation guidance and states the default behavior. It does not explicitly contrast itself with fx_rate or say when this alternative should be chosen over that one, so it falls short of a full 5.

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