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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false and openWorldHint=false, so the mutation profile is covered externally. The description usefully adds the return shape (created mailboxes with ids and full addresses), but says nothing about collision behavior when a name already exists, partial failure across a batch, or what happens if neither input mode is supplied.

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 short sentences, front-loaded with the action, then the input modes, then the return value. No filler and nothing that could be trimmed without losing information.

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?

With five optional parameters, no output schema, and annotation coverage of the safety profile, the description supplies the return contract and the input-mode rule, which is nearly everything needed. It is only slightly short on batch/collision and empty-input edge cases.

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 baseline is 3. The description restates the names-as-local-parts idea and the names/randomCount either-or, both of which the schema already documents ('used when names is not passed'), and adds no new detail on the path, firstName, or lastName parameters.

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 opens with a specific verb and resource ('Creates new GhosterMail mailboxes'), which is unambiguous and naturally distinct from the delete/list siblings. It never names a sibling or explicitly contrasts with one, so it stops short of a 5.

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 states the two mutually exclusive creation modes ('Pass either names ... or randomCount'), which is useful call guidance. However, it gives no when-to-use context versus alternatives (e.g., why create individual local parts instead of random ones) and no preconditions such as whether a name must be unused.

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