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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds real context on top: a live outbound connection to port 25 and explicit reassurance that no message is delivered. It does not mention firewall blocking or timeouts, so it stops short of a 5.

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 sentences, front-loaded with the action and followed by the output list and scope caveat. No filler or restatement of the title.

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 no output schema, the description usefully enumerates what is reported. It leaves out failure modes (port 25 blocked, no MX, TLS handshake failure), which would matter for an open-world network probe, but the essentials are present.

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 0% for the single `domain` parameter. The description implies the domain is used to locate mail servers (MX resolution), which is a genuine addition beyond the bare string schema, but it doesn't clarify whether bare domains vs. email addresses are accepted.

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 concrete action (connect to the domain's mail servers on port 25) and the exact outputs (banner, EHLO response, STARTTLS support). This clearly separates it from mail-sending operations and from policy-record checks like check_mta_sts, though it never names a sibling explicitly.

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?

"No mail is sent and no recipient is tested" bounds the scope usefully, implying this is a non-intrusive capability probe. However, it never says when to pick this over check_tls_configuration or check_mta_sts, nor any prerequisite such as the domain needing MX records.

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