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

There are no annotations, so the description carries the full burden. It mentions the possible statuses but does not disclose error behavior for invalid IDs, whether the status is real-time, or if any side effects occur. For a mutating tool this would be critical, but for a status read it's still incomplete.

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 a single sentence that front-loads the key information (status retrieval and possible values) and includes no filler. It is concise and scannable.

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?

Given the simplicity (one parameter, no output schema), the description is mostly adequate but lacks details on the return format or error scenarios. It does enumerate valid statuses, which partially compensates for the absent output schema, but an agent might still be unsure whether the response is a plain string or a structured object.

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?

The schema covers 100% of the parameter (id) with a description 'Fax-id.' The tool description adds 'per id,' which simply restates the schema. No additional meaning is provided, so the baseline of 3 is appropriate.

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 states the tool's function: it returns the delivery status of a fax by ID, with specific status values (queued/sending/success/failed). This distinguishes it from sibling tools like fax_confirm or fax_quote, which serve different purposes.

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?

No guidance is provided on when to use this tool versus alternatives. The description only states what it does, not the context for invoking it or any prerequisites. Sibling tools are not mentioned, leaving the agent to infer usage from the name and description.

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