reply

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

Annotations already establish that this is a non-read-only, non-idempotent, open-world action, and the description adds useful behavioral detail beyond them: the original is quoted below the reply, threading headers are set, and the agent should confirm with the user before sending. It does not cover rate limits or delivery behavior, but the key side effects are disclosed.

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 compact sentences, front-loaded with the core action and scope. Each sentence adds operational value: reply mode, threading behavior, required content, and confirmation guidance.

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 an open-world send action with annotations and a rich schema, the description covers what the agent needs: reply-vs-replyAll behavior, threading, quoted original, required body content, and a user-confirmation safeguard. No output schema exists, but return-value explanation is not necessary for successful invocation.

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 high at 88%, so most parameter meaning is already documented structurally. The description still adds important context not captured by the schema's required list: that body or htmlBody must be supplied, and that messageId for threaded replies should come from get_thread.

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 states a specific verb and resource ('Replies to a message') and immediately distinguishes the two modes (sender vs. everyone with replyAll). It also distinguishes this from competing actions like send_message and forward by describing reply-specific behavior such as quoting the original and setting threading headers.

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 gives explicit routing guidance: use get_thread and the latest message id to reply within a thread. It also states the body/htmlBody requirement and a safety condition ('Confirm with the user before sending'), leaving little ambiguity about when and how to use the tool.

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