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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds genuinely useful behavior beyond that: it states an empty result is returned when no numbers exist, which helps the agent interpret output, though it omits pagination or ordering 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?

Three short sentences with the core purpose front-loaded. The trailing 'Voodoo SMS REST: GET /numbers' is somewhat redundant developer metadata but is compact and not distracting.

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?

With no parameters, no output schema, and annotations covering the read-only safety profile, the description provides enough context to call the tool and interpret an empty response. Minor gaps like result ordering or volume limits are low-impact here.

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?

There are zero parameters, so the baseline is 4. The description adds nothing about parameters because none exist, and it does not need to.

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 ('List the Virtual Mobile Numbers'), defines the acronym, and explains their purpose ('used to receive SMS'). An agent can distinguish this from sibling list tools such as list_inbox or list_blacklist by the resource alone.

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 implies usage (checking purchased numbers) but gives no explicit when-to-use, prerequisites, or alternatives. For a simple zero-parameter list tool this is adequate but leaves the agent to infer context.

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