Simulate checkout payment (sandbox only)

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

Annotations already indicate readOnlyHint=false (mutation). The description adds that marking as paid triggers 'checkout.completed' and errors on live checkouts. It mentions required scope but does not elaborate on idempotency or other side effects.

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 two concise sentences, front-loading the key action and constraints. No wasted words; every sentence adds value.

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 simple sandbox simulation tool with one parameter, the description covers purpose, usage context (sandbox only), required scope, and expected error for live checkouts. The output schema exists but is not needed for completeness.

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 coverage is 100% with description and pattern for 'checkout_id.' The description reinforces that it must be a sandbox checkout, adding value beyond schema. No further parameter details needed.

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 verb 'simulate payment' and the resource 'checkout,' specifically for sandbox environments. It distinguishes from siblings by noting that live checkouts return 'sandbox_only,' making the purpose unambiguous.

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 specifies that the tool is for sandbox only and requires 'merchant_write' scope. It implies not to use on live checkouts by stating they return 'sandbox_only,' but does not explicitly list alternatives or when to use among sibling tools.

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