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

The annotations only provide title/details metadata, so the description carries the full burden of behavioral disclosure. It adds practical operational context: pricing, x-credit-token auth option, free-ail allowance, no wallet/API key required, and a concrete 122-country coverage scope. No side effects are implied, and there is no contradiction with the annotations.

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 description is front-loaded with the core question and purpose, then covers output contents, the key distinction, coverage count, and required input/pricing/auth. Every sentence contributes actionable information; there is no filler or repetition.

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?

Given a single required parameter and no output schema, the description is complete: it specifies the input, what data the agent can expect (rails, currencies, limits, asset/network counts), the use case, and the operational constraints (coverage, pricing, auth). An agent has enough to decide whether to call it and what it will receive.

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?

The input schema already documents the only parameter, country, as an ISO country code. The description merely repeats that country is required input without adding format details, defaults, or examples, leaving the schema description to carry the semantics. This meets the baseline but adds no extra value.

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 states a clear, specific purpose: a feasibility check for fiat-in and cash-out rail coverage by Coinbase in a country, including currencies, limits, assets, and networks. It distinguishes this from a quote or execution tool, and the phrase 'feasibility check before you ask a user for money' makes the resource and verb unambiguous.

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 clearly says when to use it: as a pre-flight check before requesting payment, especially to distinguish card-rail countries from crypto-transfer-only countries. It does not explicitly name an alternative like onramp_quote or state when not to use it, so it falls just 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.