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

The annotations already flag destructiveHint=true, but the description adds a critical behavioral disclosure beyond the annotations: 'Everything in it is public to any caller.' That privacy warning is non-obvious and important. It still does not explicitly say that setting the voicemail overwrites existing content, so it is not a 5.

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?

The description is front-loaded and efficient, using three short sentences with no filler. The opening identifies the resource, the middle explains content, and the final sentence documents the toggle. Minor explanatory phrases like 'what callers hear when you're not listening' are useful rather than wasteful.

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 four-parameter mutation tool with no output schema, the description covers the essential purpose, privacy implications, and the `on` toggle. The schema carries most parameter detail, and annotations carry destructive/idempotent hints. It could more explicitly state what happens when voicemail is turned off or overwritten, but it is broadly complete enough to invoke 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 75%, so the baseline is 3. The description adds meaning beyond the schema for the undocumented `on` parameter by saying 'Turn it on or off with on,' and it reinforces the public nature of `facts` and `greeting`. The `secret` parameter is not mentioned in the description, but the schema already explains it well.

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: set your own line's voicemail. It clarifies what the voicemail is for (what callers hear when you're not listening) and identifies the core content fields (greeting and facts). It does not explicitly differentiate itself from siblings like leave_message or answering_brief, so it falls short of a 5.

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?

Usage is implied by 'what callers hear when you're not listening' and 'Turn it on or off with on,' which tells the agent this configures voicemail behavior. However, there is no explicit when-to-use guidance, no exclusions, and no named alternatives among the many sibling tools.

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