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

Annotations already provide readOnlyHint=true, idempotentHint=true, and destructiveHint=false stanchion. The description adds value by explicitly stating 'Side effects: none (read-only)' and specifying the return type as a base64 TIFF page in structured output, which is useful beyond the annotations.

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 tight sentences, no wasted words. The main action is front-loaded, and the side-effect note is separated clearly. Every sentence earns its place.

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, well-typed download operation with full schema coverage, annotations, and an output schema, the description is nearly complete. The only missing context is explicit guidance about choosing between this and sibling file-retrieval tools, which is a minor gap given the low complexity.

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%: fax_id, user_id, and page_num are all documented in the schema. The description adds no further parameter detail; baseline of 3 is appropriate because the schema already carries the full load.

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 ('Download'), a precise resource ('a single page from a fax file (TIFF)'), and the output format. This clearly distinguishes it from siblings like get-file (whole file) and get-fax-thumbnail (thumbnail image).

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 implies usage—when you need just one page of a fax—but does not explicitly mention alternatives or when-not-to-use. With many sibling download tools (get-file, get-fax-thumbnail, get-fax), explicit routing guidance would improve this.

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