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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false, so the 'Read-only' sentence adds nothing. The description does add real behavioral context beyond annotations: prices are in USD cents (a units detail that prevents a 100x interpretation error) and the checkout price may differ locally. That is exactly the kind of context annotations can't carry.

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?

A single front-loaded sentence conveys purpose, pricing unit, and content. The trailing 'Read-only.' repeats the readOnlyHint annotation and is the only wasted element.

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 no parameters, full annotation coverage, and an output schema describing the return, the description needs only to frame the resource and flag non-obvious semantics — it does both via the USD-cents/local-price caveat. Nothing essential to invoking the tool is missing.

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?

The tool takes no parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The pricing-unit note is the closest analogue to parameter guidance and is handled in the description.

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 ('plans VoiceLabs offers') with enough content detail — pricing plus inclusions — to distinguish it from sibling list_* tools like list_api_keys or list_captures. It is clear but doesn't explicitly contrast against an alternative tool.

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: an agent would call this when it needs plan/pricing information. There is no explicit when-to-use or when-not-to-use guidance, and no sibling is named as an alternative, though for a zero-parameter read-only catalog tool the ambiguity is low.

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