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

With no annotations, the description carries full responsibility for behavioral disclosure. It explicitly mentions the cost (0.50 USDC per-action via x402), auto-expiry (default 24h), and the plaintext access for the owning wallet. It also states receive-only, which is a key behavior. It does not cover all edge cases (e.g., payment failure handling, idempotency), but the provided context is substantial and actionable.

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 focused sentences: purpose and ideal use, return value, and behavioral characteristics (expiry, read access, cost). No wasted words; the description is front-loaded with what the tool does and who should use it. Each sentence adds essential information for an agent deciding to invoke the tool.

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?

The description covers key contextual points: use case, return value, expiry, access model, and cost. However, it does not mention the two-step payment flow (first call to receive instructions, second call with payment), which is only in the schema. It also omits any reference to related tools like email_read_messages for consuming the inbox. These gaps prevent a 5, but the description is complete enough for a straightforward create operation with a clearly scoped purpose.

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%, with both 'payment' and 'ttl_seconds' already documented in the input schema. The description echoes the default TTL (24h) and adds cost context, but it does not materially enhance parameter understanding beyond what the schema provides. Baseline 3 is appropriate given the high schema coverage.

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 uses a specific verb ('Provision') and a distinctive resource ('disposable, receive-only email inbox'), clearly distinguishing it from the sibling tool email_create_inbox. The mention of 'temp' and 'auto-expires' reinforces the temporary nature, 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 provides clear usage context: 'ideal for receiving a one-off verification or order-confirmation email during a checkout/signup flow.' This implies when to use the tool, but it does not explicitly name alternatives (e.g., permanent inboxes via email_create_inbox) or state when NOT to use it, so it stops short of a perfect 5.

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