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

Annotations declare the safety profile (destructiveHint=true, readOnlyHint=false, openWorldHint=false), and the description adds substantial behavior beyond them: mailbox selection, threading headers, reply target, quoting of the prior message, and the mandatory two-step confirmation gate. This is exactly the kind of context a write tool benefits from.

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?

Front-loaded with the purpose, followed by precise operational details and the confirmation flow. Four short sentences, none wasted.

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?

No output schema exists, so the description must cover the interaction model, and it does via the preview/confirm_token flow. Minor gap: id and the exact effect of text/quoting behavior could be stated explicitly, but overall an agent can call this correctly.

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 only 33% (confirm_token is documented in the schema). The description reinforces confirm_token semantics and implies text is the reply body and id is the thread, but it never explicitly defines id or text, so it only partially compensates for the low coverage.

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?

Specific verb+resource ('Answer a thread' / 'Sends...') and rich scoping detail (sends from the conversation's mailbox, in-thread via In-Reply-To/References, to the last writer). This clearly separates it from the read-oriented siblings like get_thread and label_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?

Describes the confirmation workflow in detail (first call previews + returns confirm_token; call again with the token to send), which is the key usage pattern an agent needs. It does not, however, advise when to prefer this over e.g. get_thread first to read context, so it stops short of explicit alternatives/exclusions.

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