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

With no annotations, the description carries the behavioral disclosure burden. It does this well by disclosing a concrete failure mode (422 when the domain is not verified), the existence of an address before MX is configured, and the fact that it receives nothing until then. It omits side-effect details like idempotency or permissions, but covers the most decision-relevant behaviors.

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 front-loads the purpose, but it repeats the exact phrase 'receiving on an unproven domain is relay' in consecutive sentences. This redundancy wastes space and makes the wording less crisp; the third sentence adds no new information over the second.

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 simple three-parameter create tool with no output schema, the description covers the prerequisites, failure mode, and the important 'address exists but receives nothing until MX points' behavior. The only notable omission is what a successful response returns, but the rest of the context is enough for an agent to invoke it correctly.

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?

Schema description coverage is 100%, so the schema already documents all three parameters. The description adds minor context for domain (verified/active status, MX requirement) but does not substantially explain local_part or organization_id beyond what the schema provides.

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 first sentence is a specific verb+resource statement: 'Create a receiving address on a verified sending domain.' It clearly identifies the action, the object created, and the key prerequisite, and it differentiates this from sibling tools like inbox_get, inbox_disable, and domain_verify without needing their schemas.

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 gives clear conditions for use: the domain must already be verified/active, and mail delivery requires the MX record to point to the platform's inbound. It does not explicitly name an alternative tool (e.g., domain_verify for unverified domains), so it falls short of the explicit when/when-not/alternatives bar, but the context is otherwise strong.

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