list_phones

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

The annotations already declare readOnlyHint=true, so the safety profile is covered; the description adds genuinely useful context by disclosing that authentication is required and that this tool is unavailable to a session-less caller. It still says nothing about ordering, pagination or how many results to expect.

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 core action is front-loaded in one sentence, with the access requirement isolated in a clearly labeled block. The ACCESS block is slightly wordy for a simple list tool, but no sentence is 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 and no output schema, the only real burden on the description was stating the scope and any preconditions, both of which it covers. It could go further by hinting at what a phone entry contains or whether the result set is bounded, but nothing essential to calling it correctly is missing.

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 there is nothing for the description to disambiguate and the baseline for a parameterless tool applies. No misleading parameter language is present.

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 all phone numbers' — scoped to the authenticated account. Among the many adjacent list_* siblings (list_emails, list_api_keys, list_circles), the phone resource is unambiguous and there is no competing tool that lists phone numbers.

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 clearly states the prerequisite context ('needs a Proof account') and two concrete paths to satisfy it (set PROOF_API_KEY and restart, or sign in with start_login then retry). It does not state any when-not condition or contrast with siblings such as get_current_user, but the invocation path is fully spelled out.

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