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

Annotations already declare readOnly, idempotent, closed-world and non-destructive behavior, so the safety profile is covered. The description adds that pricing comes from XipFax's price list and excludes plan pricing, but says nothing about currency, tax, or whether the quote is binding.

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?

A single efficient sentence with no filler. The phrasing is slightly indirect ('The price of sending...' rather than 'Quotes the price...'), but it is front-loaded and compact.

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?

With an output schema present, return values need no explanation, and annotations cover the safety profile. For this simple one-parameter quote tool the description supplies enough context, though noting currency or that the quote targets non-plan pricing only would close the remaining gap.

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% and the single 'pages' parameter is already documented with its 1–250 range. The description only restates the page-count concept, adding no format or constraint detail beyond 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?

The description specifies the resource (one fax, N pages, XipFax, no plan) and that it returns a price from the price list, which distinguishes it from send_fax_link and find_fax_number. It states the returned value rather than using a direct verb like 'calculate' or 'quote', but the intent is unambiguous.

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?

The phrase 'without a plan' implies a scope condition, but there is no explicit when-to-use or when-not-to-use guidance and no mention of alternatives for plan-based pricing. Usage is inferable from context rather than stated.

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