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

Annotations only declare write and non-destructive; the description adds the behavior an agent actually needs: the password is randomly generated, returned once, and must be relayed to the customer because it will not be shown again. It further discloses that duplicate addresses are not pre-checked, that creation is rejected if the address exists, and that the existing mailbox is left untouched and this is not a failure.

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?

Three sentences, action first, then credential handling, then the duplicate-address caveat, then the inventory alternative — every sentence carries information and is front-loaded. Slightly verbose with the reassurance clause ('das ist keine Störung') but still efficient.

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 mutation tool with no output schema, the description supplies the crucial output context (password is returned in the response, once) and the failure semantics (existing address causes rejection, not corruption). An agent has everything needed to call it correctly and to advise the customer.

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 both parameters are fully documented in the schema, including local_part character rules and examples. The description adds no parameter-level detail beyond that, so the baseline 3 applies.

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 states a specific verb and resource ('Legt ein neues E-Mail-Postfach auf einer Domain an'), which an agent can distinguish from siblings like reset_email_password or set_email_alias without opening the schema. It also names get_email_accounts as the related read tool, sharpening the boundary.

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 routes the agent to get_email_accounts for checking the existing inventory and explains that no pre-check happens on create, which is clear context for when this tool is the right choice. It stops short of explicitly contrasting creation with adjacent siblings such as setup_email_provider or set_email_forwarding, so it is not a full when/when-not treatment.

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