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

Annotations already flag this as a non-read-only but non-destructive, open-world operation; the description adds real value by saying it validates the PDF, returns id/sha256/page count, never transmits, and requires the document:write scope. Consistent with destructiveHint=false since it only creates an artifact.

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 tight sentences: the two input modes first, the return/validation behavior second, the 'never sends' guardrail and scope last. No filler and everything is front-loaded.

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 return values need not be explained, yet the description still names id, sha256 and page count helpfully. The remaining gap is the missing rule on which of the five optional parameters to supply and what filename does.

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 0%, so the description must carry the parameter burden, and it does map text/Markdown/HTML/upload_id to their roles. However, it never mentions 'filename' and never states that the four content parameters are mutually exclusive or that exactly one is expected, leaving a 5-parameter, zero-required-parameter tool ambiguous.

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?

States a specific verb and resource plus the two input modes ('create a document to fax from text, Markdown or HTML' or 'register a completed REST upload by upload_id'). The 'Never sends' clause and the document:write scope cleanly separate it from send_approved_fax and preview_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 'Never sends' statement clearly signals this is the preparation step rather than the delivery step, giving the agent usable context for when to call it. It stops short of naming the sibling that actually sends or previews, so the routing is implied rather than explicit.

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