Send an email

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

Beyond the annotations, the description reveals that sending is irreversible, requires user confirmation, is gated by an environment flag, and enforces recipient allowlisting. It also explains reply threading/filling behavior. This is rich contextual disclosure that helps the agent anticipate real-world consequences.

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 tightly written sentences. The most important safety warning is front-loaded, followed by enabling conditions and a specific usage pattern. There is no filler or repetition of schema details.

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 9-parameter tool, the description covers the key operational constraints: side-effect irreversibility, user confirmation, environment gating, allowlist enforcement, and reply behavior. The schema covers parameters, and an output schema exists, so nothing critical is missing.

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%, so the baseline is 3. The description adds meaningful semantics for reply_to_uid, explaining that it threads the reply and auto-fills recipient and subject. This goes beyond the schema's simple field descriptions.

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 opens with 'Send an email', a specific verb and resource. It further differentiates itself by highlighting irreversibility and the reply behavior, which separates it from sibling tools like save_draft and read_email.

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 description gives clear context: confirm content first, sending only works when EMAIL_ALLOW_SEND=true, allowlist requirements, and how to reply via reply_to_uid. It does not explicitly contrast with save_draft, so it misses the full 'when to use vs alternatives' guidance.

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