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

With no annotations, the description carries the safety profile and states 'Read-only.' It also discloses the returned fields, which helps the agent understand the result. It does not mention pagination, ordering, rate limits, or auth requirements, but for a zero-parameter account listing this is a minor gap.

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 short, front-loaded, and every sentence earns its place. It states the resource, the returned fields, the purchasing boundary, and the read-only nature without unnecessary prose.

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 list with no output schema, the description is nearly complete: it names the tool's scope, return fields, and safety profile. Missing pagination or output-shape details are minor for this simple listing operation.

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 parameter semantics are not applicable and the baseline is 4. The description adds meaning about the returned data fields rather than input parameters, which is appropriate here.

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: lists phone numbers already on the account. It also enumerates the fields returned and clarifies that buying numbers happens elsewhere, so it is clearly a read-only listing tool rather than a purchase or management tool.

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 makes the intended use clear: retrieving existing account phone numbers. It explicitly excludes buying numbers by saying that is done in the app, though it does not name a specific sibling alternative for purchasing or other phone-related operations.

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