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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals the exact effect (pushes expires_at 7 days further, stackable, no cap), ownership requirement, that expired inboxes cannot be revived, and the cost (0.50 USDC via x402). This is strong transparency for a paid mutation tool, though it omits error scenarios or return format.

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 sentences, front-loaded with the primary action, and each clause adds essential information (duration, stacking, ownership, expiration handling, cost). No wasted words; it reads naturally and is efficient.

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 tool with no annotations and no output schema, the description covers the core purpose, constraints (owner-only, expired cannot be revived), cost, and alternative action. It does not describe the response format or what happens on success/failure, but the input schema is simple and the behavioral context is strong.

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?

The input schema already covers both parameters (inbox_id, payment) with descriptions, so the baseline is 3. The description adds value by explaining the effect of calling repeatably ('stackable, no cap') and tying the payment param to a per-action cost of 0.50 USDC, reinforcing ownership constraints. This goes beyond what the schema states.

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 action: 'Rent another 7 days on a live disposable temp inbox' with a specific verb and resource. It distinguishes from sibling tools like email_create_temp and phone_extend_temp by focusing on extending an existing temp inbox, and it explicitly mentions 'Owner-only' and the alternative for expired inboxes.

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 context for when to use this tool: to extend a live, owned temp inbox by 7 days. It explicitly excludes expired inboxes ('cannot be revived') and directs users to email_create_temp for that case. It does not explicitly list all alternative tools, but the guidance is sufficient for the main use case.

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