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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds one genuinely useful trait, 'Free' (no cost), but omits other relevant behavior such as whether the result reserves the name or how it is reported.

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?

Two short sentences, purpose front-loaded and the pre-purchase timing stated second, with no filler. Every clause contributes.

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 one-parameter read check with no output schema, the description covers purpose, timing and cost but says nothing about the shape of the result (e.g. boolean availability) or whether a positive check holds the name. Those are the remaining gaps an agent would care about.

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% and the single parameter is fully documented with length and allowed characters, so the schema carries the load. The description's mention of 'local part' mirrors the schema description rather than adding new syntax or constraint detail.

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?

Names a specific verb (check) and a precise resource (a name's availability as the local part of an address), which an agent can distinguish from create_inbox. It stops short of naming a sibling tool explicitly, so it is clear but not fully differentiated within the toolset.

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 phrase 'before buying an inbox' supplies clear timing/context, telling the agent to call this prior to create_inbox. It gives a positive condition but no explicit exclusions or statement of what to do instead on failure.

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