Send email from alias

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

Annotations already declare readOnlyHint=false and openWorldHint=true, but they do not convey that this produces irreversible real-world side effects. The description adds that it 'sends real mail' and names the required credentials (RESEND_API_KEY or Cloudflare Email Sending), which is meaningful context an agent cannot infer from the annotations. It stops short of describing the response payload or failure modes.

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 short sentences, front-loaded with the action and scope, then prerequisites, then the safety guard. No redundant restatement of the title and no filler.

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 4-required-parameter tool with annotations and no output schema, the description covers purpose, credentials, and the irreversibility warning. It omits what a successful call returns (e.g., a message id) and whether the alias must pre-exist, which would fully close the loop.

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 75%, so the schema already documents to, text, and alias; only subject lacks a description. The description adds the semantic point that alias is the visible sender identity while the real address stays hidden, but offers no format or constraint details. Baseline 3 is appropriate with the schema doing most of the work.

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 (send) and resource (plain-text email) with a distinguishing scope: FROM one of the user's aliases so the real address stays hidden. This is clearly separable from the sibling tools (create_alias, list_aliases, set_alias_enabled, recent_messages), none of which send mail.

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?

Gives an explicit precondition/exclusion: 'only call it when the user asked to send this exact message,' which guards against an agent inventing outbound mail. It does not discuss ordering relative to create_alias or what to do if the alias doesn't exist, but the core when-to-use guidance is strong.

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