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

Annotations already declare non-readonly, open-world, non-idempotent, and non-destructive. The description adds meaningful context beyond those: it limits the action to one short message and discloses the privacy behavior ('sealed for that line's AI alone'). It does not describe delivery confirmation or failure handling.

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 precondition, with no redundant or filler text. Every clause adds usable information.

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?

Covers precondition, message content, and privacy behavior for a four-parameter mutation tool with no output schema. It relies on the schema for secret and intent details, which is reasonable, though it could say more about what happens after delivery.

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. The description goes further by giving content guidance for the message parameter ('Say who you are, who you're calling for, and what you need'), which adds meaning beyond the schema's character limit.

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 ('Leave one short message') and scopes it to a precise precondition: a line whose voicemail answered, described as a call that came back away. This cleanly separates it from live-call siblings like say and from voicemail retrieval.

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?

Gives a clear triggering condition ('a call that came back away, with voicemail'), so an agent knows when this applies. It does not explicitly name alternatives such as say for live calls or voicemail for listening, leaving that inference to the agent.

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