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

Annotations already declare read-only, open-world, idempotent, and non-destructive behavior; the description adds concrete protocol details: port 25, EHLO, STARTTLS attempts, banner/TLS/rDNS reporting, and no mail sent. This is strong disclosure beyond annotations, though timeout and port-25 blocking caveats are omitted.

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 compact sentences, front-loaded with the connection behavior and ending with the key no-mail guarantee. No redundant or filler wording.

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-only SMTP probe with no output schema, the description adequately covers the mechanism, target, and reported categories. Minor operational details such as timeout behavior, which MX records are tested, and port-25 blocking are omitted but not essential for selecting the 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?

There is only one parameter, and the schema fully documents it at 100% coverage, including the note that it is a mail domain rather than a mail server name. The description reinforces that the domain is used to locate MX records but adds no new parameter-level syntax or constraints.

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 precise action sequence: connect to MX servers on port 25, send EHLO, try STARTTLS, and report banners, TLS, and reverse DNS. This clearly distinguishes it from siblings like mx_check and ssl_check, even without naming an alternative.

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 implies usage for diagnosing SMTP server reachability and TLS behavior, and the note that it never sends mail is a useful safety cue. However, it gives no explicit when-to-use versus siblings such as mx_check, reverse_dns, or ssl_check, and no exclusions.

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