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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description's added value is its disclosure of return contents: per-number outbound notes (provider, missing SIP trunk) and a billing_warning for overdue renewals. That is meaningful context beyond the annotations, and the 'does not test live carrier health' caveat prevents a wrong expectation about freshness of carrier status.

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?

A single front-loaded sentence names the resource first, then the returned detail, then the exclusion. It is dense but every clause carries information; no filler.

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?

With no parameters, no output schema, and read-only annotations, the description covers what an agent needs: what is returned, the advisory fields (outbound notes, billing_warning), and the one thing it does not do. Only the absence of explicit sibling routing keeps it from full completeness.

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. There is nothing for the description to disambiguate, and it correctly makes no parameter claims.

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 the phone numbers on the account') plus the key relation ('which assistant each one is bound to'). It doesn't explicitly name the sibling it differs from (e.g., call2me_search_numbers, which presumably finds available numbers rather than owned ones), so differentiation is inferable but not stated.

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 line 'It does not test live carrier health' gives one negative boundary, but no positive when-to-use guidance and no named alternative for carrier health checks or number search. An agent must infer the routing from sibling names alone.

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