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

Annotations already declare destructiveHint=true, openWorldHint=true, and non-idempotency, so the safety bar is partly covered. The description adds a genuinely non-obvious trait the annotations cannot express: the call is a dry-run preview by default and only destructive when confirm=true. It does not cover auth/credential requirements or send rate limits.

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, front-loaded with the action and immediately followed by the gating rule. Every clause carries information an agent needs; nothing is redundant with the title or schema.

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 an output schema present, return-shape detail is not required, and the description still flags that the return may be a preview rather than a send result. Missing pieces are SMTP configuration/credential assumptions and recipient-format expectations, which are minor for a 5-parameter tool with only one unconventional field.

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 description coverage is 0%, so the description carries the burden, and it fully explains the one non-obvious parameter (confirm). However, 'to', 'cc', 'subject' and 'body' are left purely to their titles, and recipient formatting (single vs. comma-separated, whether cc accepts a list) is unaddressed despite being the most likely invocation error.

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 specific verb and resource ('Send email') plus the transport ('via SMTP'), which is enough to separate it from the read/search/list siblings in the same domain. An agent can identify the tool's function without opening the 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?

Explicitly gives the condition that switches behavior: confirm=true to actually send, otherwise a preview is returned. That is real when-to-use guidance. It stops short of naming alternatives or exclusions (e.g., that this is the only write path vs. flag_message/move_message), so it is clear but not fully routing-aware.

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