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

With no annotations provided, the description carries the burden of transparency. It discloses the key side effect: 'Debits advertiser credits into escrow,' and explains the purpose of couponCode and postbackUrl for attribution. It does not mention reversibility or failure behavior, but covers the most critical mutation.

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 concise at roughly three sentences and front-loads the main purpose. The '[Buy]' prefix and alias list add a bit of bulk, but overall no sentence is wasted; it packs essential guidance into a compact format.

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 tool with 16 parameters and no output schema, the description covers the core flow (booking, escrow, optional attribution, follow-up coupon) but omits many optional fields and does not indicate what the response contains. It is sufficient for basic use but leaves gaps for edge cases.

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 description coverage is low at 38%, so the description must compensate. It adds meaning to adUnitType (prefer agent-directed types) and budgetCredits (escrow), and clarifies couponCode/postbackUrl roles. However, many parameters like feedType, productId, durationDays, and product snapshot fields are not explained 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?

The description opens with 'Create an ad campaign booking on a placement,' a specific verb and resource, and distinguishes itself from create_coupon by noting it should be used after booking. It also lists aliases buy_campaign and buy_placement, clarifying sibling tool names.

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?

Explicit guidance is given on when to use this tool: 'prefer agent-directed cpr/cpia/cppromo/cpd to reach the agent's own recommendation/decision path instead of a human click.' It also tells the agent to 'use create_coupon to attach an agent-readable promo payload for cppromo units' after booking, providing a clear alternative for a related task.

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