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

Annotations already mark this as a non-read-only, open-world, non-destructive operation. The description adds valuable non-annotation context: it is legacy, uses upstream balances, skips normal credit UX, and exposes provider-era assumptions.

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 two tightly written sentences with zero filler, and the most important warning is front-loaded. The bolded alternative name makes routing information easy to scan.

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?

Output schema and annotations cover return values and safety profile, and the description covers purpose, routing, and legacy behavior. However, with 0% schema description coverage, the complete absence of parameter semantics leaves an important gap for a tool that requires service and optionally country.

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 0%, so the description carries the burden of explaining the two parameters. It does not mention or clarify either country or service, leaving required parameter meaning entirely undocumented.

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 identifies this as a legacy rental that uses upstream balances rather than normal credits, and it names the sibling alternative ucode_sms_rent_with_credits. The specific resource is implied by the title and name, but the description itself does not explicitly say 'rent a phone number,' so it is clear but not maximally specific.

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 gives explicit when-not guidance: 'Do not use for ChatGPT end users.' It also names the preferred alternative for those users, ucode_sms_rent_with_credits with packages, which lets an agent route correctly without inspecting sibling schemas.

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