Create an in-app purchase

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

With annotations only declaring readOnlyHint=false and destructiveHint=true, the description adds real behavioral value: 'idempotently' tells the agent retries are safe and a duplicate product_id will not double-create, and 'Pro feature' signals an entitlement precondition. It stops short of explaining what a failed/partial create leaves behind or how the created IAP is identified in the response.

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 brief sentences, zero filler, and the most decision-relevant facts (idempotent create, one-time, USA price) are front-loaded. Nothing is repeated that structured fields already state verbatim.

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 10-parameter mutation tool with no output schema, the description covers the essentials: idempotency, product scope, and entitlement gating, with all field detail delegated to a fully covered schema. It could go slightly further on post-creation expectations (e.g. that a review screenshot still has to be set via set_iap_review_screenshot before submission), which is the one workflow gap.

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 100% and every field is individually documented (type enum, price_usd, product_id, length caps), so the schema carries the parameter burden. The description's mentions of purchase type and USA price restate the schema rather than adding format constraints or defaults, so the baseline 3 applies.

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 ('Create ... a one-time in-app purchase'), narrows the variants (non-consumable or consumable), and pins the pricing rule ('with USA price'). This plainly distinguishes it from the sibling create_subscription, which covers recurring purchases.

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 rather than stated: 'one-time' implies this is the non-recurring counterpart to create_subscription, and 'Pro feature' hints at a gating/precondition. There is no explicit when-to-use/when-not or named alternative, so the agent must infer the boundary.

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