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

Beyond the readOnlyHint and non-destructive annotations, the description adds important behavioral context: it sends nothing, is free, validates the destination and document, and counts pages. This helps the agent understand side effects and preconditions without guessing.

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?

Three short, front-loaded sentences with no filler. The core purpose is stated first, followed by concrete behavior and an explicit usage rule.

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 quote tool with read-only annotations and fully documented parameters, this description covers what the tool does, what it returns, that it has no side effects, and when it should be called. No critical information is missing for correct invocation.

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%, so the schema already documents all three parameters. The description mentions validating 'the destination and the document,' which loosely maps to the parameters, but it does not add meaningful semantics 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 opens with a specific verb and resource — 'Price a fax before committing to anything' — and clarifies the tool's exact job: validate destination/document, count pages, return an exact total plus a payment link. This clearly distinguishes quote_fax from send_fax and the status/receipt siblings.

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 states 'Always call this before send_fax,' giving the agent a direct rule for when to use this tool. It also frames the tool as a pre-commitment step, which implies the alternative is the actual sending operation.

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