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

Adds behavior beyond the annotations: it discloses a side effect ('Refreshes the stored price quote when pricing has changed') and explicitly negates the dangerous actions ('does not create an order or mail a letter'). This explains why readOnlyHint is false, which the annotations alone cannot 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?

Four sentences, front-loaded with the return contract, then the pricing side effect, then usage, then the negative scope. Each sentence earns its place, though the return-value sentence is somewhat dense.

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?

An output schema exists, so return values need not be re-explained, yet the description usefully links the returned total to send_letter's confirm_total_cents. For a single-parameter preview tool, nothing needed to call it 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?

With one required parameter and 0% schema description coverage, the description carries the burden but never describes draft_id's format or where it comes from. The context makes the meaning inferable, but there is no added parameter-level detail.

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 ('Return a link to the rendered PDF of a draft') plus the two satellite outputs (page count, total price). It also distinguishes itself from send_letter, so an agent can tell the preview step apart from the send step without opening the 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 says to use it 'before calling send_letter' to show the user what will be printed and what it costs, giving clear sequencing. It does not discuss alternatives such as get_pricing or when a preview could be skipped, so it stops just short of full when/when-not guidance.

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