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

Annotations already declare the operation read-only, non-destructive, and closed-world, so the description only needs to add context, which it does: an authentication/ownership prerequisite and an explicit statement that no side effects (port submission, service cancellation) occur. That no-op guarantee is exactly the kind of reassurance a cautious agent needs before calling.

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?

Two short clauses, with the access precondition front-loaded before the operation, and nothing redundant or padded. Every phrase adds either a constraint or a behavioral guarantee.

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 single-parameter read-only check with full annotation coverage, the definition supplies the caller prerequisite, input scope, and the fact that nothing is mutated. The only gap is what the check yields (a boolean portability verdict, reasons for ineligibility, etc.), which no output schema covers either.

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?

Schema coverage is 0% for the single `number` parameter, but the description compensates somewhat by specifying the value is an owner-provided US business number, constraining the expected input. It still omits the expected string format (E.164 vs. national formatting) despite the schema's maxLength of 30.

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 definition gives a specific verb and resource ("Check the owner-provided US business number for portability"), and its negative clause ("does not submit a port or cancel current service") separates it from port-submitting siblings such as prepare_number_port or activate_phone_number. It stops short of naming those alternatives, so the differentiation is implied rather than explicit.

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?

"Owners only (needs sign-in)" states the required caller context up front, and the closing sentence makes clear this is a pre-check, not an action. It does not name which tool to use instead once the number proves portable, leaving that routing to inference.

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