mail_inbox

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

With no annotations provided, the description carries the full burden and does well: it discloses that this is a purchase with a real financial cost (0.5 USDC on Base via x402), a fixed 7-day lifetime, and a capability limit (receive-only, so no sending). It omits what the purchase returns and any refund/idempotency behavior beyond what the parameter description already states.

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?

A single front-loaded sentence with the verb and resource first and cost details trailing in parentheticals. The stacked parentheses ('(paid) (costs 0.5 USDC ...)') are slightly awkward but nothing is wasted.

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 purchase tool with no annotations and no output schema, the description covers what it is, what it costs, and its lifetime, but not what the agent receives after purchase or how the resulting inbox is consumed (the mail_messages path). Adequate but leaves a real gap around post-purchase workflow.

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% and the single parameter's own description already explains duplicate-purchase semantics, so the description adds nothing parameter-specific. Baseline 3 applies when the schema does the heavy lifting.

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 ('Buy a receive-only email inbox') with concrete scope (7 days, receive-only, paid). The closest sibling, mail_messages, is presumably the read side of this inbox, but the description never names or contrasts against it, so an agent must infer the relationship.

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?

Gives cost and payment rail but no when-to-use guidance: nothing says to use this when a disposable inbox is needed, nor how to proceed afterward (e.g., via mail_messages). The confirmNewPurchase parameter carries the only behavioral guidance, and it lives in the schema, not the description.

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