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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safe-read profile is covered. The description adds genuine context beyond that: the payment rail is USDC on Base, no login is required, and it applies only without prepaid credits. It does not discuss rate limits or quote validity, keeping it out of 5.

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?

Two sentences, front-loaded with the core purpose (exact USDC price for one number) and followed by the prerequisite. No filler or redundant restatement.

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 read-only quote tool with safety already covered by annotations and no output schema, the description supplies what an agent needs: what is quoted, in what currency/network, and the input dependency. The one gap is that it never states the quote is informational only and does not rent the number.

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 both 'service' and 'country' are already documented in the schema. The description reinforces the source of the 'service' code but adds no format or syntax detail beyond what the schema provides, so the baseline 3 applies.

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 verb and resource: an exact USDC (Base) price quote to rent one number for a service/country. The 'without prepaid credits' clause meaningfully disambiguates it from credit-based siblings like ucode_sms_prices and ucode_sms_rent_with_credits. It stops short of naming an alternative sibling explicitly, so it lands at 4 rather than 5.

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?

Gives clear context for when this tool applies (pay-as-you-go quoting without prepaid credits) and a concrete prerequisite: pull the 'service' code from ucode_find_numbers and supply a countryId. It stops short of explicit when-not-to-use guidance or naming the credit-based alternative to avoid.

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