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

Annotations already declare the write/open-world/destructive profile, so the bar is lower, and the description still adds real value: it discloses that the server generates recipients, subject and quoted text, and it imposes a confirm-before-calling guardrail. It does not say whether the send is irreversible or what happens if the conversation has moved on.

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?

Three short sentences, front-loaded with the action and the reason it differs from a generic send, then parameter guidance, then the safety instruction. No waste and no restatement of the title.

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?

For a mutation tool with no output schema, the definition covers the key unknowns an agent faces: what it must supply, what the server derives, how recipient scope is controlled, and that user confirmation is expected. Nothing required for a correct call is missing.

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 100%, so the baseline is 3, but the description adds meaning beyond the schema by explaining the contract behind body (only the body is supplied because everything else is derived) and tying replyAll to its behavioral effect on the original's recipient list.

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?

States a specific verb and resource ('Reply in an existing conversation') and immediately clarifies the mechanism that separates it from send_outlook_message and create_outlook_draft: Outlook constructs recipients, subject and quoted original server-side. An agent can distinguish this tool from its siblings without opening any schema.

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 scopes usage to an existing conversation and states the replyAll condition plus a human-confirmation requirement, which is clear operational context. It stops short of explicitly naming the alternatives (send_outlook_message for new mail, create_outlook_draft to stage without sending) or stating when not to use it.

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