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

Annotations already declare readOnlyHint=false and destructiveHint=false; the description adds real behavioral context beyond them — the 30-minute validity window, accepted formats (PDF, JPG, PNG, camera), and 10 MB size cap. It also states the tool sends nothing, which is useful reassurance for a preparatory action.

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?

One dense sentence that front-loads the primary action before the constraints and follow-up. Every clause carries information (validity, formats, size, next step, cost), though the density makes it slightly harder to scan than separate lines would.

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?

With no output schema, the description carries the return-value burden, and it does so implicitly — upload_url is referenced and upload_id is mentioned as the input to send_fax. That covers the essentials for a zero-parameter tool, leaving only minor ambiguity about the exact returned field names.

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 and the schema coverage is 100%, so there is nothing for the description to clarify. Baseline 4 is appropriate for a no-parameter tool.

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 ("Erstellt einen sicheren Einmal-Upload-Link") and immediately binds it to a purpose ("für das Fax-Dokument"). It also names the follow-up sibling send_fax, so an agent can place it in the fax workflow without opening the schema.

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?

Describes the workflow clearly: user opens upload_url, uploads the file, then call send_fax with the upload_id. The "Kostet nichts und sendet nichts" line clarifies the tool's role versus the send step. It lacks an explicit when-not-to-use or a direct sibling comparison, but the sequencing leaves little ambiguity.

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