reply_to_message

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

No annotations are provided, so the description carries full burden. It only discloses one limitation: no attachments. It does not mention whether the reply is sent immediately or saved as a draft, whether it quotes the original message, what happens to the original message (e.g., flagged as replied), or any required permissions. This is insufficient for an agent to understand side effects.

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 consists of two short sentences: the first states the purpose, the second notes a key limitation. It is front-loaded and contains no extraneous information. Every sentence earns its place.

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 5 required parameters, no output schema, and no annotations, the description is incomplete. It does not explain the result of the operation (e.g., does it send immediately? create a draft?), nor does it describe the side effects on the original message (e.g., marking as replied). The only behavioral detail is the attachment limitation. The agent lacks necessary context for proper usage.

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?

The input schema has 100% description coverage with clear explanations for all 5 parameters. The tool description adds no additional parameter-level meaning beyond the schema. According to the rules, baseline is 3 when schema coverage is high, and the description does not significantly augment it.

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 the action ('Reply to an existing email message') and the resource. It distinguishes from sibling tools like 'forward_message' and 'send_message' by the nature of the action. It also mentions a specific limitation (no attachments). However, it could be more precise about what 'reply' entails (e.g., creating a reply in the same thread).

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?

No guidance is provided on when to use this tool versus alternatives like 'forward_message' or 'send_message'. There is no mention of prerequisites (e.g., message must exist, user must have access) or conditions under which reply is appropriate. The only contextual clue is the attachment limitation, which is a behavioral constraint, not usage guidance.

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