Check the SMTP connection

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable protocol-level context beyond those annotations: TLS negotiation, authentication, connection close, and the explicit guarantee that no message is sent. This clarifies the side-effect profile (network connection but no data mutation) and helps the agent understand what the tool actually does at runtime.

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 sentences, each earning its place: the first states the core action, the second draws a critical boundary (no message sent), and the third gives routing guidance. Zero wasted words; the most important information is front-loaded.

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 zero-parameter tool with a rich annotation set (read-only, idempotent, non-destructive) and an output schema present, the description covers everything an agent needs: what it does, what it doesn't do, and when to choose it. There are no gaps in prerequisites, side effects, or return expectations.

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?

The tool has zero parameters, and the schema coverage is 100% (nothing to document). Per the baseline for parameterless tools, a 4 is appropriate — the description doesn't need to compensate for any undocumented parameters because there are none.

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 states a specific verb and resource: 'Opens a connection to the SMTP server, negotiates TLS and authenticates, then closes it again.' It clarifies scope with 'No message is sent,' distinguishing it from mail-related siblings. The configuration-vs-delivery framing further separates it from validate_recipients and preview_mail without needing to open any schema.

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 final sentence gives explicit situational guidance: 'Use it to tell a configuration problem apart from a delivery problem.' This tells the agent when the tool is appropriate. It doesn't explicitly name sibling alternatives or state when not to use it, but the context is clear enough that an agent can infer the routing decision.

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