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

Annotations already indicate this is a safe read operation. The description adds useful behavioral information: the receipt is only available once the fax reaches a final state, and its purpose is verification. This goes beyond the annotations without contradicting them.

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, focused sentences with no filler. The core function is front-loaded, the availability constraint is stated, and the practical use case is given immediately.

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 simple single-parameter read-only tool, the description is nearly complete: it explains what to expect, when it is available, and why to call it. It could mention behavior when the fax is not in a final state, but this is a minor gap given the annotations.

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?

There is only one parameter, fax_id, and it is self-explanatory. However, schema description coverage is 0% and the description does not explicitly explain that fax_id identifies the fax for which the receipt is requested, though it implicitly refers to a completed fax.

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 clearly identifies the tool's resource: a verifiable delivery receipt for a completed fax. It differentiates from siblings like get_fax_status, quote_fax, and send_fax by emphasizing proof of completed delivery rather than current status or sending a fax.

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 clear usage context: use it only after the fax has reached a final state, and use it to prove the workflow finished. It does not explicitly name alternatives, but the context makes the intended timing clear relative to get_fax_status.

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