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

Annotations declare readOnlyHint=false, destructiveHint=false, openWorldHint=true, so the write/safety profile is already covered. The description adds real behavioral context beyond that: 'Draft creation never pays', the exact return payload (order ID, total, hosted checkout URL, checkout session), the MPP challenge/preview behavior, and that signatures may be typed or drawn. It stops short of stating auth requirements or rate limits.

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?

Front-loaded with the action and the returned artifacts, then the checkout/MPP branches. Every sentence carries routing or behavioral information; the MPP and x402 sentences are dense but each names a distinct flow rather than padding.

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 20-parameter, nested-object tool with an output schema, the description covers the payment lifecycle, the signature capability, and sibling routing well. The remaining gap is the address-selection parameters and mailing options (mail_class, certified, double_sided), which are left entirely to a sparse schema.

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 15% across 20 parameters, so the description carries a heavy burden. It does clarify payment_protocol and buyer_email and notes that letter text and signatures are supplied inline, but it never explains the Address/Container/Manual address_type enums or how address_id vs address_text vs address_manual differ — the single most ambiguous part of the schema.

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 ('Prepare letter text for mailing' returning an order ID), and clearly distinguishes itself from create_pdf_upload ('no PDF upload or browser is needed') and create_machine_order ('For x402, use postalform.create_machine_order'). An agent can route among the sibling draft creators without opening a 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?

Explicitly lays out the branches: use complete_checkout after buyer approval with a Stripe shared payment token, otherwise present the hosted checkout URL; set payment_protocol=mpp plus buyer_email for MPP and then call postalform.pay_order; use create_machine_order for x402. When-to-use and which-alternative are both spelled out.

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