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

Annotations only cover the safety profile (readOnlyHint=false, openWorldHint=true, destructiveHint=false). The description adds real lifecycle context beyond them: the call returns a payment link and the piece only mails after payment, which shapes how the agent should sequence pay_order. It stops short of covering idempotency or failure behavior.

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 tight sentences with the core action and sizes front-loaded, then layout, then the payment dependency. No filler or restatement of the tool name.

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?

With no output schema and nested to/from/content objects, the description supplies the essentials: what is produced (payment link), what goes where on the card, and the payment gate. It omits retry/idempotency guidance and any pointer to get_pricing for cost.

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 33%, so the description must compensate, and it partly does by mapping front (image URL or headline) vs back (message and addresses). However, idempotency_key and the to/from object structure get no explanation, and the headline/image precedence is only implied.

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 ('Create a postcard order') and pins down the scope with the two supported sizes and the returned payment link. It is distinguishable from create_letter by resource, but never names or contrasts the sibling, so it falls short of a 5.

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?

Usage is implied: this is the tool for mailing a postcard, and 'Mails only after the user pays' tells the agent the order is not fulfilled immediately. There is no explicit when-to-use vs create_letter/pay_order, nor any stated prerequisite about gathering pricing first.

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