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

Despite annotations only covering the safety profile, the description adds substantial behavioral context: this tool NEVER mails anything and NEVER charges anyone, payment happens only later on the review page by the recipient, and printing/mailing is conditional on that payment. It also discloses the pricing model ($16.17 with ERR, $13.18 without, per-page surcharge) and the exact return artifact (a review link showing document, recipient, service, total). That is well beyond what readOnlyHint=false and destructiveHint=false convey.

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?

It is long, but it is front-loaded with the one-call promise and return value before drilling into input modes and addresses, and nearly every sentence carries operational content. Minor redundancy in restating pricing and the review-page flow, and the pricing detail could arguably be shortened, but nothing 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 28-parameter, zero-required tool with a rich output schema, the description covers everything an agent needs: the four mutually exclusive document-input paths, address-block parsing with field precedence, what happens to missing data, the exact return artifact, and the hard constraint that nothing is charged or mailed. Return values are described succinctly even though an output schema exists.

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 already 89%, so the schema carries most param documentation. The description still adds genuine meaning: the precedence rule ('naming the fields yourself always wins over the block'), the mutual exclusivity of letter_text/document_text/document_base64, the distinction between a composed letter and an already-finished document, and that page_count only matters with person_has_pdf. It goes beyond the schema rather than repeating it.

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 opening sentence gives a concrete verb and resource: it 'turns a letter or document in this conversation into a priced, ready-to-send USPS Certified Mail item.' The scope (U.S. destinations, review-page payment, never mails) is specific enough that an agent knows exactly what will exist after the call. It never names or contrasts with its sibling quote_certified_letter, so sibling differentiation is left to inference.

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?

It states clearly when nothing else is needed first ('no account, no sign-up, no card, no second call') and gives explicit routing rules among the four document-input modes, including a preference ('Prefer document_text whenever you can read the document at all'). It also explains that missing fields are collected later and do not block the call. The one gap is that it never says when to use the sibling quote_certified_letter instead.

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