Reply to an email

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

Annotations already signal a non-read-only, non-idempotent operation, and the description adds the behavioral guarantee of correct threading. It does not disclose whether the reply is sent immediately, how recipients are resolved, or any side-effect caveats beyond what the schema already exposes.

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?

A single front-loaded sentence communicates the core operation and its notable options without wasted words. It is appropriately sized for the tool's complexity.

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?

The schema and output schema cover parameters and return shape, but the description leaves room for ambiguity between sending a reply and creating a draft, and gives no routing guidance relative to send_email or create_draft. For a side-effectful email action this is a notable gap.

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 100%, so every parameter is already documented. The tool description only restates optional history, attachments, and reply-all without adding semantics beyond the schema.

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 uses a specific verb (Reply) and resource (email), and adds distinguishing behavioral details: correct threading, optional history, attachments, and reply-all. This differentiates it from sibling send_email, which lacks reply threading semantics.

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 action itself implies usage: it is for responding to an existing email rather than composing a new one. However, the description provides no explicit when-to-use guidance and does not mention alternatives like send_email, create_draft, or schedule_email.

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