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

Annotations already declare destructiveHint=true, idempotentHint=true, readOnlyHint=false, and openWorldHint=true, and the description reinforces rather than contradicts them while adding context the annotations cannot convey: the call only returns a payment link, no paper is printed or postage bought until payment completes, and the operation becomes irreversible at print time. It also discloses a failure mode (quote mismatch aborts the send) and the domestic-address restriction.

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 dense but front-loaded: action and artifact first, then the payment-link caveat, then usage triggers, then the email exclusion and address scope, then prerequisites and the irreversibility warning. Every sentence contributes a distinct fact and no sentence is filler.

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 destructive, open-world mutation with an output schema (which removes any need to describe return payloads), the description covers prerequisites, cost-confirmation flow, domestic scope, irreversibility, and the not-an-email distinction. Nothing an agent needs in order to decide and call correctly is missing.

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%, so all three parameters are already fully documented in the schema, including the idempotency-key reuse behavior and the confirm_total_cents match requirement. The description largely restates these ('confirm_total_cents matching the current quote', 'requires a draft_id from create_draft') and adds only the linkage to create_draft as genuinely new meaning. Baseline 3 is appropriate when the schema carries the parameter burden.

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 and resource ('Create an order for a real, physical letter through the United States Postal Service') and immediately scopes it against the obvious confusable sibling by declaring 'This is NOT email — use an email tool for email.' An agent can distinguish this from create_draft, preview_draft, or an email tool without opening any schema.

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 an explicit trigger ('whenever the user asks to mail, post, send by post, or physically send a letter'), an exclusion ('This is NOT email'), a geographic limit ('US domestic addresses only'), and hard prerequisites (a draft_id from create_draft, a confirm_total_cents matching the live quote). This is exactly the when/when-not/alternatives coverage the dimension asks for.

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