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

With no annotations, the description carries full responsibility for behavioral disclosure. It clearly warns about credit spending ('SPENDS CREDITS (2 per contact)') and describes the core side effect of purchasing and snapshotting contacts. It could mention reversibility or failure behavior, but the cost warning and prerequisite cover the most critical behavioral traits.

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 concise sentences with no filler. The most important information (credit cost) is front-loaded, followed by action and a clear prerequisite. Every phrase earns its place.

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 single-parameter purchase action with no output schema, the description covers the essential context: cost, effect, and approval condition. It does not describe the return value or behavior when the set is already purchased, but the low complexity and clear precondition make this a minor omission.

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 describes only an 'id' string with no description. The description hints that the id identifies 'the set' being purchased, which adds some meaning, but it never explicitly states 'id is the audience set identifier.' Since schema coverage is 0%, the description must compensate more fully for parameter semantics.

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 ('Purchases') and resource ('the set'), and clarifies the side effect: 'snapshots its contacts into the workspace.' It also implicitly distinguishes itself from preview_buy_audience_set by framing itself as the actual purchase action. This is unambiguous and easy to differentiate from siblings.

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?

Provides explicit when-to-use guidance: only call after the user reviewed preview_buy_audience_set output and explicitly approved the cost. This is a strong precondition that prevents premature or unauthorized spending. It does not explicitly discuss alternatives like launch_audience_set, but the prerequisite is clear and valuable.

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