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

Annotations already declare readOnlyHint=true and destructiveHint=false, covering the safety profile. The description adds critical behavioral context: the URL is 'short-lived', informing the agent to use it promptly. This goes beyond the structured fields and is genuinely useful. No contradiction with 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?

The description is a single, concise sentence that front-loads the core functionality. Every word contributes value, with no filler or redundancy. It is appropriately sized for a simple retrieval tool.

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 tool's simplicity, the presence of an output schema (so return values are documented elsewhere), and annotations covering safety, the description covers all necessary context. The short-lived URL note is the only addition beyond schema, and it is included. No missing information for correct invocation.

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 describes both parameters as 'UUID value wrapper' with 100% coverage. The description adds no additional meaning about the parameters—it does not explain their roles beyond what the schema already provides. Since schema coverage is high, the baseline is 3, and the description does not compensate further.

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 returns a short-lived signed S3 URL for a rendered PDF invoice. The verb 'get' and resource 'Invoice PDF URL' are explicit, and it distinguishes from siblings like invoice_get_invoice (which returns invoice data) and invoice_get_list_invoices (which lists invoices). No ambiguity about what this tool does.

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 provides no explicit guidance on when to use this tool versus alternatives. While the name and purpose are self-evident for retrieving a PDF URL, there is no mention of prerequisites (e.g., invoice existence) or conditions (e.g., expiry handling). It does not state when not to use it, but the simplicity of the operation mitigates this gap.

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