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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true. The description adds meaningful context beyond those: the pricing tiers, that validation of number and PDF occurs, that it sends nothing, and that the response includes a quote_id and payment link. It does not cover quote expiration or error behavior, so it falls short of 5.

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?

The description is dense and front-loads pricing, which dominates the first sentence. The more actionable instruction, 'Call before send_fax,' is relegated to the end; reordering would improve it, but every sentence still carries useful information.

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?

There is no output schema, so the description appropriately names the return values (quote_id, payment link). It covers cost, validation, and sequencing, but does not address quote validity duration or failure modes, leaving a minor gap for a pre-payment validation step.

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 100%, and the schema documents all three parameters, including that destination is US/Canada only. The description only implicitly references the parameters through 'validates the number and PDF,' adding little beyond the schema, so baseline 3 applies.

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 specific verbs and resources: returns price, validates number and PDF, returns quote_id and payment link. This clearly distinguishes it from siblings send_fax, get_fax_status, and get_fax_receipt, which do not price or validate documents.

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 tells the agent to 'Call before send_fax,' which establishes both when to use it and its relation to the natural next tool. 'Free; sends nothing' further clarifies that it is a safe, non-sending check.

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