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

The description explicitly states 'Side effects: queues outbound fax for delivery', which explains why the annotations mark destructiveHint=true — a real fax will be transmitted to actual recipients. This adds specificity beyond the bare annotation and there is no contradiction with any annotation flag.

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 short sentences with no filler: the core mechanism is front-loaded, the critical parameter constraint follows, and the side effect is stated last. This is efficient and well-ordered, though the second sentence could arguably be folded into the schema note.

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 an 11-parameter tool with nested objects, the description is thin — it explains the core concept and side effect but gives no guidance on the many optional parameters (options, cover_page, send_time, user_id) or how they interact. However, the output schema exists and schema coverage is 100%, so the schema carries most of the burden, leaving only a moderate 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%, so the baseline is 3. The description adds minimal value beyond the schema: it clarifies the role of from_fax_id ('reusing an existing fax file reference') and emphasizes that 'to must be an array', but both points are already well-documented in the property descriptions. It does not compensate further for the 11-parameter surface.

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 states a specific verb (Queue) plus resource (outbound fax) plus mechanism (reusing an existing fax file reference via from_fax), which distinguishes it from the sibling send-fax-uploaded that starts from an uploaded file. It does not name the sibling explicitly in the purpose statement, but the mechanism is specific enough for an agent to tell it apart.

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 description gives no guidance on when to use this tool versus alternatives such as send-fax-uploaded or update-fax, and mentions no exclusions or prerequisites. The only usable note is the parameter-level warning that 'to must be an array of destination numbers', which is format guidance, not when-to-use guidance.

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