retell_create_phone_number

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

With no annotations, the description must disclose behavioral traits, but it only states the core action. It does not mention billing/financial implications, side effects, irreversibility, or what happens if area_code is omitted. The word 'purchase' hints at cost but is not explicit.

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 captures the essential purpose and key optional behavior with zero unnecessary words.

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?

The tool is relatively simple with complete schema documentation, but the description omits important contextual details for a purchase action, such as cost implications, default area code behavior, or return value. It is adequate but not thorough.

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 input schema has 100% description coverage, with each parameter clearly documented. The description adds a minor context about binding to an agent, but it does not go beyond what the schema already provides, so it earns the baseline 3.

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 clearly states the action (purchase) and resource (new US phone number), with an optional binding to an agent. It distinguishes itself from sibling tools like retell_list_phone_numbers and retell_delete_phone_number by focusing on creating a new 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?

The description conveys when to use it (when you need to purchase a new number) but provides no explicit guidance on alternatives or exclusions, such as using retell_import_phone_number for existing numbers. The context is implied, not explicit.

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