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

Annotations only say readOnlyHint=false, destructiveHint=false, idempotentHint=false. The description adds genuinely new behavioral facts: the link is one-time, expires after 30 minutes, creating it sends nothing and costs nothing, and it is a handoff mechanism feeding send_fax. This answers the natural 'does this have side effects or cost?' question for a non-read-only tool.

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 sentences, front-loaded with what is created and its constraints, then when to use it over send_fax, then the follow-up flow. No filler; every clause carries operational information.

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 parameterless tool with no output schema, the description covers constraints (expiry, size, formats), the selection rule versus the sibling, and the return values and their downstream use. Nothing needed to invoke or chain it correctly 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?

The tool takes zero parameters, which sets the baseline at 4. The description does add value by naming the two output artifacts (upload_url and upload_id) and how they are consumed, partially compensating for the absent output schema.

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 (creates a secure one-time upload link) with scope details: 30-minute validity, accepted formats (PDF, JPG, PNG), and 10 MB cap. It is instantly distinguishable from siblings like send_fax and get_fax_status.

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?

Explicitly names the alternative and the selecting condition: use this for files on the user's device or chat attachments not available via send_fax's "file" parameter. It also spells out the required follow-up workflow (user opens upload_url, then send_fax accepts the returned upload_id).

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