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

With annotations already declaring destructiveHint=true and non-idempotent, the description adds useful context: it sends in the person's name, requires approval of the exact text, and enumerates failure cases (message not found, empty text). It does not state that the send is irreversible, though the destructive hint covers the safety profile.

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 tight sentences, front-loaded with the operation, then the approval precondition, then failure behavior. No filler.

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 two-parameter mutation with no output schema, the description covers purpose, precondition, and failure modes, and annotations cover reversibility and openness. Missing only param format detail and any mention of the side effect beyond sending.

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 0%, so the description must compensate. It implies text must be non-empty ('text is empty' failure) and that message_id targets a single Inbox message, but gives no format for message_id or note the 20000-char limit on text. Partial compensation only.

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 (SENDS an email) and resource (reply to one Inbox message) and the scope ('as a reply to one Inbox message'), which cleanly separates it from siblings like list_inbox and read_inbox_message. An agent can identify the operation without opening the 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?

Explicitly gates use on 'the person's approval of the exact text', which is real when-to-use guidance. It does not name alternatives (e.g., read_inbox_message to obtain the message first), so it falls short of full routing guidance, but the precondition is clear.

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