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

Annotations already mark this as read-only and idempotent, and the description adds substantial behavioral context beyond that: it distinguishes automaticSizingCeiling from explicitCountCeiling, explains that only 'balanced' mode has the explicit ceiling, and discloses the MODE_CAP refusal behavior and the fallback to memberCap. This goes far beyond what the annotations provide.

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 with a bold, actionable directive, followed by precise, non-redundant details about the returned ceilings and failure behavior. Every sentence earns its place, and the warning about expensive mid-creation failures justifies the tool's importance without fluff.

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 read-only, optional-parameter tool, the description fully covers when to call it, what it returns, how the mode parameter alters behavior, and what error occurs on exceeding a ceiling. Even without an output schema, it enumerates the key returned fields and their semantics, leaving no critical gap for an agent deciding to invoke this tool.

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 schema documents the optional mode parameter at 100% coverage, and the description adds meaning by explaining what each mode ceiling represents and how mode choice affects which ceiling applies. It clarifies the consequences of omitting memberCount and of stating a size, making the mode parameter semantically richer than the schema alone.

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 uses a specific verb and resource ('returns the ceilings that apply to THIS account') and clearly frames the tool as a pre-creation check for Audience sizes. It distinguishes itself from creation and listing siblings by emphasizing that it reports limits rather than creating or listing anything.

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 explicit when-to-use triggers: 'Call this before creating an Audience whenever a size is in play', with concrete examples like a named number, 'as many as possible', or choosing a creation mode. It also actively recommends the tool over guessing, explaining the cost of being refused mid-creation.

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