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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description's 'nothing is charged' usefully reinforces that a cost estimate has no financial side effect, and naming the GET endpoint adds a little context, but return shape and the effect of optional fields on the estimate are undisclosed.

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?

Two sentences, front-loaded with the purpose and the no-charge guarantee, then the option-string constraint. No filler, and the endpoint is demoted to the tail.

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 13-parameter, 8-required tool this covers the two things that most easily go wrong: sourcing valid option strings and the fact that nothing is created. With no output schema, the description could say what the estimate returns (total, breakdown by component), and it is silent on the four optional parameters.

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 coverage is 100%, so baseline is 3, but the description adds real meaning beyond the schema: the example values in the schema are illustrative only, and the description pins them to get_product_options as the authoritative source. It also signals quantity is a cost driver, though it says nothing about the optional parameters (payment_type, number_of_pages, non_standard_quantity, international_quantity) that meaningfully change the estimate.

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 ('Estimate the cost of a mailing from its print options and quantity') and adds the key scope qualifier that nothing is created or charged. It doesn't explicitly differentiate from click2mail_get_job_cost, the nearest sibling, but the input-based framing makes the distinction inferable.

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 a concrete precondition: 'Use the exact option strings from click2mail_get_product_options', which is exactly the kind of routing an agent needs for an enumeration-heavy tool. It stops short of naming exclusions (e.g. use get_job_cost when a job already exists).

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