Create alias contact

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

Annotations cover the safety profile (readOnly=false, destructive=false, openWorld=true), and the description adds value beyond them: the response semantics (reverse_alias_address, existed=true meaning nothing was created) and the premium-plan requirement. This is meaningful behavioral context an agent would not get from structured fields alone.

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?

Purpose is front-loaded, followed by input format, response semantics, and a caveat. Each sentence carries distinct information with no filler, though it is slightly dense in the final sentence.

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?

Both required parameters are documented, and with no output schema the description compensates by explaining the meaningful return fields and the existed flag. Nothing an agent needs to invoke or interpret this call correctly is missing.

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 coverage is 100%, so the baseline is 3, but the description adds usable syntax guidance: bare address vs RFC-5322 display form with a concrete example. That goes beyond the schema's terse parameter descriptions.

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?

States a specific verb and resource ('Create a contact (reverse alias) on an alias') and explains the underlying concept so an agent understands the object being created. It is clearly distinguishable from siblings like contact_list, contact_set_blocked, and contact_delete.

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 a clear use case ('so the user can send mail from the alias to that contact while keeping their real mailbox hidden'), which tells the agent when this tool applies. It stops short of naming alternatives or exclusions, but the context is unambiguous.

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