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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the bar is lower, yet the description adds real semantic context: it explains what automaticSizingCeiling vs explicitCountCeiling bound, notes that only 'balanced' carries an explicit ceiling, and states that in deeper modes a stated size is bounded by memberCap alone. It does not address auth requirements, so 4 rather than 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 purpose is front-loaded in sentence one, and the exclusionary sentences ('These are per-Audience sizes, not workspace capacity...') earn their place by preventing a real misreading. Some sentences are dense and the last two overlap conceptually, so it is efficient but not maximally tight.

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 the return values needn't be explained, yet the description supplies the boundary conditions an agent needs to interpret them correctly and explicitly rules out what the numbers are not (workspace capacity, credits, reservation, remaining balance). For a one-optional-parameter read-only tool, nothing needed to call it correctly 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?

Schema coverage is 100% and the single enum parameter is already documented ('Report only this creation mode. Omit to see every mode.'). The description elaborates mode-related behavior indirectly (which ceiling applies per mode), which adds marginal value, but the parameter contract itself is fully carried by the schema — the baseline 3.

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 first sentence names a specific verb and resource — it returns the audience size ceilings for the authenticated account before an Audience is created — and enumerates the concrete ceilings (plan cap, custom-size maximum, per-mode ceilings). This clearly distinguishes it from creation siblings like create_audience_from_brief and recalibrate_audience, so an agent can route to it without opening the schema.

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 triggering conditions: 'whenever a size is named, "as many as possible" is asked for, or a creation mode is chosen.' That is clear when-to-use context, but no when-not conditions and no named alternative sibling for comparison, so it stops short of the top band.

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