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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds genuinely useful context beyond that: it states the payload contains NO secrets and that sensitive keys are referenced by TitleSecrets entry name only, while public keys/certs are safe to expose. It could still note the return shape/pagination, but the disclosure value is real.

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?

Front-loaded with the core 'GET ONLY the Purchase field' scope, followed by contents, sibling distinctions, and a security note – each sentence carries information. It runs long, but little reads as filler, so the size is mostly justified.

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 no output schema, the description carries the burden of explaining what is returned, and it does so thoroughly by enumerating the field's contents. Combined with the sibling distinctions and the no-secrets clarification, an agent has everything needed to call it correctly.

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?

Only one parameter (title_id) with 100% schema description coverage, so the schema already documents it fully. The description adds no syntax or scope detail beyond what the schema provides, making the baseline 3 correct here.

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 precise verb+resource: it returns ONLY the 'Purchase' field of TitlePublicConfigurationModel, then enumerates exactly what that field holds (IAP SKUs, rewards, subscriptions, audience gates, receipt verification). It explicitly distinguishes itself from two named siblings, Store and Premium, so an agent can select it without opening either 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?

Names the alternatives it is not (Store for virtual-currency shops, Premium for the entitlement itself) and clarifies the boundary between them. It lacks an explicit 'when to call this vs. save_purchase' framing, but the read-only scope plus the named distinctions give clear context.

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