List messaging numbers

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

Annotations already declare readOnlyHint and openWorldHint, and the trailing 'Read-only.' merely restates readOnlyHint without credit. The description does add genuine behavioral value by disclosing the result shape (capabilities plus latest message per number), which is not in the annotations, but it says nothing about account scope or pagination.

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, front-loaded sentences with no padding. The only wasted clause is 'Read-only.', which duplicates the readOnlyHint annotation rather than adding 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 zero-parameter read tool with no output schema, the description covers what the tool returns (numbers, capabilities, latest message) and the intended next step. What is missing is scoping detail such as whether results are paginated or limited to the primary account versus sub-accounts.

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 of 4 applies. There is no parameter surface the description needs to compensate for, and it correctly does not invent or imply any inputs.

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 numbers on this account that can send and receive SMS/MMS') plus the returned payload (capabilities and latest message). However, it never distinguishes itself from the closely named sibling list_phone_numbers, so an agent must guess which list is which.

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?

'Use one as send_message `from`' gives a concrete workflow trigger that ties this tool to a downstream sibling. It stops short of stating when not to use it (e.g., versus list_phone_numbers or search_available_numbers), so it is clear context without exclusions.

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