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

Annotations already cover read-only, idempotent, non-destructive and closed-world, so the safety profile is settled. The description adds genuinely new behavior: the owner must complete setup themselves, nothing is registered on their behalf, and no email is captured. It also discloses the hosting arrangement (Surfing Dog at inbox.<domain>), which is context the schema cannot carry.

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?

Roughly four short sentences with the core fact front-loaded and no filler. The sentence 'The open-source inbox to run themselves is named too' is awkwardly passive and leaves unclear where that name surfaces, a minor structural blemish rather than bloat.

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?

An output schema exists, so return values need not be explained, and the single required param is fully specified. The description covers purpose, the no-side-effects guarantee, and the follow-up verification step. Only the ambiguous reference to a self-hosted alternative name keeps it from a 5.

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?

Only one parameter and schema coverage is 100%, so the schema already documents domain including the 'URL is read as its domain' normalization. The description adds minor value by showing how domain composes into the resulting link (inbox.<domain>). Baseline 3 applies since the schema does the heavy lifting.

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 makes clear this produces a hosted setup link at inbox.<domain> for the business owner, not a signup flow. The action verb is implied ('give the owner the link') rather than stated as 'returns a URL', but the resource and scope are unambiguous. It also names check_dns as the downstream step, which helps separate it from siblings.

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?

Explicit routing: hand the link to the owner, and use check_dns once the DNS record is in place. It also rules out a plausible misread by stating the tool 'signs no one up and takes no email'. No explicit when-not-to-use against a named alternative, which keeps it below a 5.

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