Prepare mail reply

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

The description reinforces the readOnlyHint annotation by stating it 'computes' and 'writes nothing.' It adds behavioral details such as quoting behavior ('> ' for replies, labelled forwarded blocks for forwards), subject prefix rules ('Fwd:' exactly once), and header handling (In-Reply-To/References). This goes well beyond the annotation alone.

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 front-loaded with a one-sentence summary, followed by a read-only note and a direct pointer to mail_create_draft. The Args section is cleanly formatted and every sentence adds value – no fluff or repetition of schema metadata.

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?

Given the tool has no output schema and only three parameters, the description covers the tool's purpose, output (headers and body), mode variations, and the follow-up action. It also clarifies the read-only nature, making it complete for an agent to select and invoke 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 0%, so the description compensates by defining message_id as a Message-ID from mail_search/mail_read_thread output, quote as including the original body with specific formatting, and mode with three detailed options including Mail-Followup-To semantics. Each parameter is fully explained beyond the schema's type/default fields.

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 a specific verb ('Derive') plus the resource ('reply/forward headers and the quoted or forwarded body'), clearly distinguishing it from read-only tools like mail_read_message and mail_read_thread. It also names the output artifacts (To/Cc/Subject/In-Reply-To) and the body format, making the tool's function unmistakable.

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?

It explicitly instructs the agent to pass the result to mail_create_draft for persistence, and it specifies that this tool itself writes nothing, establishing when to use it versus the draft-saving alternative. The mode parameter is explained with concrete semantics (reply/reply-all/forward) and pitfalls (honoring Mail-Followup-To), giving clear usage context.

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