List available email domains

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

The description indicates that the tool performs a list operation, which implies a read-only behavior with no side effects. However, it does not explicitly state permissions or output format, but given the simplicity, it is sufficiently transparent.

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 concise, using only two sentences to convey the tool's function and usage context. It avoids unnecessary details.

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 description provides complete context for a parameterless tool, including its purpose and when it is needed relative to sibling tools. There is no ambiguity or missing information.

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 no parameters, so there is nothing to explain. The description does not need to elaborate on any input, making it fully clear.

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 tool's purpose: to list domains available for inbox creation. It also differentiates it from create_inbox by noting that create_inbox picks a domain automatically. This makes the purpose unambiguous.

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 explicitly advises when to use the tool, namely when a specific domain is desired, and contrasts it with create_inbox's automatic selection. This gives clear usage guidance.

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