Prepare mail reply

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

Reinforces annotations with 'This is read-only: it computes... but writes nothing.' Adds behavioral details about quoting and mode differences (e.g., honouring Mail-Followup-To). No contradiction.

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?

Concise: two paragraphs total. First summarizes purpose and read-only nature. Second details parameters. No wasted words. Each sentence adds value.

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?

Fully explains all aspects for a 3-param read-only tool with no output schema. Covers parameter details, usage workflow, and behavioral nuances.

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?

Despite 0% schema description coverage, description explains all three parameters: message_id (source), quote (includes body formatting), mode (reply/reply-all/forward with specific behavior for each). Provides rich semantic context.

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?

Clearly states 'Derive reply/forward headers and the quoted or forwarded body' with specific verb (derive) and resource. Distinguishes from sibling mail_create_draft by noting it is read-only.

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?

Explicitly says 'Pass the result's To/Cc/Subject/In-Reply-To to mail_create_draft (draft tier) if you want it actually saved as a draft.' This tells when to use this tool vs alternative and explains the workflow.

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