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 real context beyond that: the account-scoped nature of the data, the exact fields each entry carries (E.164, status, 10DLC campaign), and the underlying endpoint. It omits pagination/rate-limit behavior, keeping it short of a 5.

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 zero padding; the resource scope and returned fields come first, then the practical use, then the API grounding. Nothing could be removed without losing information.

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 parameterless read with no output schema, the description adequately compensates by enumerating the returned fields and the endpoint. Only the absence of any pagination or result-size note keeps it from being fully complete.

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 takes zero parameters, so the baseline is 4. The description adds a relevant cross-tool note about the `from` field value this list supplies, which is useful framing even though there are no parameters to disambiguate.

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?

Specific verb+resource: lists the account's SMS numbers and approved alphanumeric sender IDs, with the key returned fields named inline. It is clearly distinguishable from siblings like list_fax_numbers, list_brands, and list_campaigns without opening any 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?

It gives a downstream use ('Use one of them as `from` when sending'), which implies the reason to call it, but never states when to prefer it over alternatives or any prerequisites/exclusions. Usage is implied rather than stated.

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