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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context by warning that this is a raw ID table and is only intended for legacy API pairing, which sets expectations that it does not provide user-friendly country names or rental credit details.

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 compact clauses with no filler. The core meaning is front-loaded ('Raw worldwide country id table'), the legacy-only caveat follows immediately, and the sibling routing is a single clear sentence. Every phrase earns its place.

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 zero-parameter, read-only lookup tool, the description covers what the tool is, when it should be used, and which alternatives to prefer. An output schema exists for return details, so nothing essential is missing for an agent to select and invoke it correctly.

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 tool has zero parameters and schema coverage is 100%, so there are no parameter semantics to document. The baseline of 4 applies because the description does not need to compensate for any parameter documentation gaps.

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 clearly identifies the tool as a 'raw worldwide country id table' and distinguishes it from sibling tools by noting it 'pairs with legacy APIs only.' It also names ucode_sms_summary and ucode_sms_service_detail as the better alternatives for renting, so an agent can tell this tool apart without opening schemas.

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 explicitly states when to use this tool ('pairs with legacy APIs only') and when not to use it ('For renting, use ucode_sms_summary / ucode_sms_service_detail'). Naming the alternative tools and the reason gives clear routing guidance.

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