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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered; the description adds real domain context by decoding all four lifecycle states, including that provision_failed stops billing and surfaces last_error. It says nothing about ordering, size limits, or what a fully empty list means.

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 sentences, both front-loaded: the resource and its lifecycle states come first, the two concrete use cases come second. The parenthetical status definitions each earn their place because the terms are not self-explanatory.

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 output schema, the description carries the burden of describing returns and mostly does: a list of numbers with status, plus last_error on failures. It omits what other per-number fields exist (id, phone number format, timestamps), leaving an agent to guess at the record shape.

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 schema baseline of 4 applies. The description correctly implies a no-argument full listing rather than a filtered query, but has no parameters to elaborate on.

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?

It uses a specific verb and resource ('List the phone numbers this workspace rents from DripRaven') and defines the population precisely as workspace-scoped rentals. It doesn't name the obvious sibling (search_phone_numbers) or contrast itself with buy_phone_number/release_phone_number, which keeps it out of the top band.

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 explicit triggering situations: check whether a purchase completed after the user says they paid, and find a number for WhatsApp signup. It gives no when-not guidance and never names an alternative tool (e.g. search_phone_numbers for lookups by attribute).

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