create_mailbox

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

Annotations are minimal (readOnlyHint=false, destructiveHint=false), so the description bears the burden. It discloses that mailboxes persist across sessions, returns a working address immediately, explains slug personalization (agent-<slug>@...), and notes that custom domains must be verified. No contradictions with annotations.

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?

Five tight sentences, front-loaded with the core action and usage guidance. Every sentence adds value—no filler, no redundancy. The structure logically flows from purpose to when-to-use to parameter 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?

Given 4 optional parameters, no output schema, and minimal annotations, the description covers the essential behavioral context: creation semantics, persistence, duplication consequences, and domain verification requirement. It references sibling tools appropriately. Minor gaps include lack of error scenarios or rate limits, but overall complete for a creation tool.

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%, providing a baseline of 3. The description adds meaningful context beyond the schema: clarifies that slug produces 'agent-<slug>@...', explains domain_id must come from list_domains and be verified, and notes that omitting extraction_schema_id yields cleaned messages without structured extraction.

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 starts with 'Create a NEW email mailbox this agent owns', using a specific verb and resource. It clearly distinguishes from sibling tools like list_mailboxes (which checks existing mailboxes) and list_domains (which provides domain IDs for customization).

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?

Explicitly states 'Call this when list_mailboxes shows you have no suitable mailbox yet' and warns against creating duplicates because 'mailboxes persist across sessions, so creating a second one for the same purpose strands mail in the first.' Also guides use of domain_id from list_domains for custom domains, including the verification requirement.

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