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

Although annotations indicate readOnlyHint=false and destructiveHint=true, the description adds substantial behavioral detail: test receipts vs. live x402 flow, unpaid results containing PaymentRequired, how to retry with PaymentPayload, where settlement appears in the result, and the warning never to send a private key. This is far more than the annotations alone convey and does not contradict them.

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 dense but front-loaded with the core purpose, then logically covers modes, failure handling, and retry behavior. It is longer than minimal but every sentence contributes meaningful operational context, though some details like 'REST continuation' could be trimmed without loss.

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?

Given the complexity of a payment flow, no output schema, and only four parameters, the description is highly complete. It covers error states, idempotency, retry semantics, settlement metadata, and the alternative get_order path. The only notable omission is the meaning of the 'since' parameter, which prevents a perfect score.

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 only 50%, and the description compensates well for mode, idempotency_key, and mandate-related eligibility. However, the 'since' parameter remains completely unexplained in both the schema and the description, leaving a gap for an agent trying to understand what value to provide.

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 clearly states the tool's function: purchasing a Snapshot for 0.01 USDC, and distinguishes between sandbox and live modes. This is a specific verb+resource with enough detail to identify it among siblings such as purchase_changes, purchase_evidence, and get_free_sample.

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?

The description provides explicit guidance: sandbox is default, live only applies when specific conditions are met, an unpaid result should be retried with the same tool and idempotency key, and pending orders should use get_order instead of submitting another payment. It names the alternative tool (get_order) and conveys a clear when-to-use/when-not-to-use distinction.

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