Reply to a message

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

The description adds behavioral context beyond annotations: it indicates that the tool creates a draft or sends depending on mode, that Thunderbird derives recipients/subject/quote, and that setting cc replaces derived addresses. This aligns with destructiveHint=true and provides nuance not captured by annotations.

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?

The description is four sentences with no extraneous words. The first sentence gives the core purpose and default behavior. Subsequent sentences logically detail derivation, variants, and warnings. It is front-loaded and earns each sentence.

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 13 parameters and an output schema, the description covers the main workflow but omits many parameter details. It explains the essential behavior (draft/send, derivation, reply variants) but lacks specifics on parameters like confirm, is_html, attachments, identity_id, and quote_original. The output schema presumably covers return values, so the missing param details limit completeness.

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 must compensate. It mentions message_id, body, mode, reply_all, reply_to_list, and cc but does not explain bcc, confirm, is_html, subject, attachments, identity_id, or quote_original. Many important parameters are left undocumented, forcing the agent to infer from the schema alone.

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 clearly states 'Reply to a message' and specifies that it saves a draft unless mode='send'. It distinguishes between reply_all and reply_to_list, and implies how it differs from new mail or forward tools. The verb and resource are specific and 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?

The description explains when to use the tool (to reply) and provides guidance on mode, reply_all, reply_to_list, and the implication of setting cc. It implicitly warns about overriding derived addresses. It does not explicitly mention alternatives like mail_send but the context is clear enough for an agent to infer.

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