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

Well beyond the annotations, the description discloses that this tool does not send anything itself — the recipient of the link adds pages, signs in, and pays in a browser. That human-handoff behavior is the single most important thing an agent needs to know and is consistent with readOnlyHint/idempotentHint. The downstream login and payment expectations are also surfaced, which annotations cannot express.

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 core output and followed by the input alternatives and the downstream step. No filler, and the optional detail lives in the second sentence where it belongs.

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?

An output schema exists, so the link's return value needs no explanation. For a two-optional-parameter URL generator with full annotation coverage, the description supplies the calling convention, the input alternatives, the eligibility constraint, and the human handoff — nothing an agent needs is missing.

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, but the description adds real meaning: it establishes the two inputs as alternatives ('an office ... or a fax number'), a mutual exclusivity the schema does not encode, and it constrains fax_number to the US, its territories, or Canada. The office_id origin from find_fax_number also tells the agent where the value comes from.

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 names a concrete output (a link that opens XipFax's send screen pre-filled with a fax number) rather than restating the title. An agent can tell this generates a handoff URL, not a fax send. It does not explicitly contrast itself with the sibling quote_fax, which is the one missing clarity element.

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?

It gives clear context for invoking: pass an office_id sourced from find_fax_number, or a raw US/territory/Canada fax number, and the human completes the send. That is actionable routing guidance plus a geographic eligibility rule. It stops short of stating when to prefer this over quote_fax (e.g., pricing vs. actual sending).

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