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

Annotations are absent, so the description carries the burden. It discloses that the tool lists approved and pending Sender IDs, which implies a read-only operation. However, it doesn't explicitly state that the operation is non-destructive, nor does it mention pagination, result format, or any rate limits. The description is adequate but minimal for a read-only list operation.

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 a single sentence, front-loaded with the key terms 'List approved and pending custom alphanumeric Sender IDs', which immediately conveys the purpose. It has zero waste and is appropriately sized for a parameterless list operation.

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?

Given the tool's simplicity (no parameters, no output schema, no annotations), the description is reasonably complete. It covers the what (list Sender IDs) and the scope (approved and pending, authenticated account). It could mention that it returns both statuses in one call, but that is implied by 'approved and pending.' The description suffices for an agent to call 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 no parameters, so there is nothing to explain. The schema coverage is 100% (there is nothing to cover), and the description does not mislead. A baseline of 4 is appropriate for a tool with zero parameters, as no additional parameter semantics are needed.

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 states the tool lists approved and pending custom alphanumeric Sender IDs for the authenticated account. The verb 'list' and the resource 'custom alphanumeric Sender IDs' are specific, and 'approved and pending' adds detail. It is distinguishable from siblings like list_campaigns and list_contacts by naming the specific resource, though it doesn't explicitly differentiate from similarly named list tools.

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 in the context of managing sender IDs (e.g., before sending SMS), but it does not explicitly state when to use this tool over alternatives, nor does it mention any prerequisites like authentication. Given there are no siblings for listing sender IDs, the lack of explicit alternatives is a minor gap, but the context is straightforward.

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