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

Annotations already flag destructiveHint=true and openWorldHint=true, so the safety profile is covered; the description adds genuinely new context by disclosing the auto-appended "Sent via Lodestone" footer on the Free plan and instructing the agent not to duplicate it. It also constrains content to plain text. It does not mention whether sending is reversible, rate limits, or failure behavior.

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 immediately followed by the one non-obvious behavior. Every clause carries information the agent would otherwise get wrong.

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 simple three-parameter send tool with full schema coverage and annotations, the description covers the main surprise (the footer) and the plain-text constraint. It leaves minor gaps around failure behavior and whether subject is optional, but nothing critical to invoking it correctly.

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 100%, with per-parameter descriptions for to, body, and subject, so the schema carries the parameter burden. The description adds only the indirect implication that body must be plain text and that the footer should be excluded; it gives no format or constraint detail beyond the schema.

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 ("Send a plain-text email from your connected account") that clearly separates it from the read-only email siblings (email_list_recent, email_read, email_search). It does not explicitly name an alternative outbound-channel tool, but the send action is unambiguous.

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?

There is no guidance on when to use this versus other messaging tools (beeper_send_message, telegram_send_message) or on prerequisites such as having an account connected. The only conditional statement concerns footer appending, which is behavioral, not usage-routing.

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