Get a purchase

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint. The description adds genuinely useful context beyond them: the endpoint requires OAuth and does not support API keys, which affects how an agent must authenticate. It stops short of describing return shape or failure behavior.

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?

Three short sentences, front-loaded with the operation before the auth caveat, with little waste. 'Reads account data' is mildly vague filler but the rest 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-item getter with a 100%-documented schema, full safety annotations, and no output schema, the description covers what an agent needs to call it correctly, including the OAuth caveat. The missing piece is routing guidance against list_purchases.

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%, so both parameters (account, purchase_id) are already documented in the schema. The description adds no format, default, or constraint detail beyond that; 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+resource ('Get a purchase') that reads clearly as a single-item retrieval. It distinguishes itself implicitly from create_purchase and list_purchases via the verb, but never names them, so differentiation is left to inference.

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?

There is no guidance on when to use this versus list_purchases or the other purchase siblings, and no stated prerequisites beyond auth. The 'Reads account data' sentence gestures at context but does not tell the agent when this tool is the right choice.

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