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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world, so the safety profile is fully covered and the description does not need to restate it. What it adds — that passing contact_id also returns that contact's communication style, and that the payload is advisory drafting guidance — is largely mirrored in the parameter schema and output schema. Useful framing, but not much beyond structured data.

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?

Two short sentences with no filler; the usage condition is front-loaded ahead of the return description. The opening is a grammatical fragment, which slightly reduces readability, but nothing is 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?

With an output schema present and 100% parameter coverage, the description only needs to establish when and why to call it, which it does. The remaining gap is minor: no indication of what happens when no voice profile exists for the user (new user fallback behavior).

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?

With one optional parameter at 100% schema description coverage, the schema already explains contact_id ('Optional contact API id to also fetch their communication style'). The description restates this function ('plus a contact's communication style when you pass a contact_id') without adding format, id source, or failure semantics, so baseline 3 applies.

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 names the resource (the user's voice profile) and enumerates what it returns: tone, greeting, signoff, and phrases to avoid. That is concrete enough for an agent to know exactly what it gets back, though it never explicitly differentiates itself from siblings (none of which are close competitors, so the omission is low-cost).

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 an explicit trigger condition — 'Before drafting any message for the user, when you want it to sound like them and not like a generic AI.' That is a clear, actionable when-to-use. It lacks a when-not-to-use or a named alternative, so it falls short of a 5.

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