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

Adds substantial context beyond the annotations: it discloses that processing is offline with nothing stored, that the tool is paid (0.01 USDC via x402 on three chains, no account needed), exactly how the payment challenge appears in structuredContent, and where the settlement receipt lands in result._meta. Nothing here contradicts readOnlyHint/idempotentHint.

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-loaded with the core purpose and output shape, then the payment mechanics. It is dense with parenthetical detail and the x402 paragraph is long, but every sentence carries operational information an agent needs before invoking a paid tool.

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?

There is no output schema, yet the description enumerates the return fields (10-digit national number, E.164 landline +54 and mobile +549 forms, wa.me link, is-mobile flag) plus the payment error and settlement paths. An agent has everything needed to call it and interpret both success and failure.

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 baseline is 3, and the description earns the bump by giving concrete accepted formats ('011 15 1234-5678', '+54 9 11...', '0351 4...', '15 prefix') rather than the schema's generic 'any common format'. It also implies the normalization rules applied to the input (strip trunk 0 and mobile 15).

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 gives a specific verb+resource ('Parse and normalize an Argentine phone number') and enumerates accepted input styles with concrete examples. It never names a sibling, but the resource (phone numbers vs. CBU/CUIT/dolar) makes it implicitly distinct from the other ar_* 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?

It clearly states the calling contract ('Send {phone}') and the failure path (unpaid calls return a payment-required result, sign an accepts entry and retry). It does not name alternatives or say when a different tool would be preferable, so it stops short of full when/when-not guidance.

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