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

The annotations already declare this as a read-only, idempotent, non-destructive, closed-world operation. The description adds a useful scope clarification that it does not purchase numbers, but it does not add details about permissions, pagination, or return behavior.

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 description is two short sentences, front-loads the operation, and uses the second sentence to prevent a plausible confusion with buying numbers. It is appropriately sized with no wasted text.

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 no-parameter read-only list tool with rich annotations and no output schema, the description provides enough context to call it correctly. The main scope ambiguity, purchasing versus listing bindings, is explicitly addressed.

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 has zero parameters, so parameter semantics are not a substantial burden. The description adds no parameter meaning, which is appropriate for a no-parameter list operation.

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 description uses a specific verb and resource ('List number bindings'), making the operation clear. It also distinguishes the tool from purchasing a phone number, though it does not explicitly contrast with the closer sibling actions bind_number and unbind_number.

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?

Usage is implied by 'List number bindings,' and the negative statement rules out buying numbers. However, it does not explicitly say when to use this versus bind_number, unbind_number, or other listing tools.

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