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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds a genuinely useful non-schema fact — a cost of 1 credit — but says nothing about what happens when a code is unknown, whether results are cached, or how the scam/shared classification should be interpreted.

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?

One question plus one cost clause — tight and front-loaded, with no wasted sentences. The question form is slightly informal but not misleading, and the cost is placed where an agent will actually see it.

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?

An output schema exists, so return values need not be explained, and the tool is structurally simple with only two parameters. However, with zero schema coverage the agent still lacks the input format and country-scoping behavior needed to call it correctly on the first try.

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 full burden for the two parameters and delivers nothing: no short-code format (digits only? length?), no explanation that country defaults to US, and no note that the same code can differ across countries.

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 the resource ('this SMS short code') and the exact questions the lookup answers: operator identity, legitimacy, shared vs. scam status. Against siblings like lookup_phone and lookup_domain, the resource is unambiguous, so an agent can route without opening the schema.

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?

There is no guidance on when to choose this tool over lookup_phone (which may also accept short codes) or when not to use it. The country parameter's role is never mentioned, leaving the agent to infer that a short code may be country-scoped.

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