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

readOnlyHint=true already tells the agent this is a safe read, but 'Short-lived' adds genuine value beyond the annotations by warning that the returned URL expires and must not be cached. It stops short of saying how long the link lasts, whether fetching it is rate-limited, or what happens on an unknown invoiceId.

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 sentence, zero waste, and the most decision-relevant fact ('short-lived') is front-loaded. Nothing in it is filler.

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?

A single-parameter read tool with an annotation covering safety needs little, but the two gaps that matter for correct invocation remain: where invoiceId comes from and how expiry affects downstream use of the URL. Adequate but clearly incomplete for a link-generation tool.

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 0% and the description says nothing about invoiceId – not its format, not where to obtain it (presumably list_client_invoices), not error behavior for a malformed ID. With one required parameter and no schema documentation, the description needed to compensate and does not.

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 resource (invoice PDF) and, unusually, the exact return shape: a download link rather than the PDF itself. It is distinguishable from list_client_invoices and resend_invoice_email, though it never names those siblings to make the boundary explicit.

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?

Usage is only implied by the noun phrase 'download link for an invoice PDF' – an agent can infer it's the fetch-a-link step, but there is no statement of when to use it versus list_client_invoices (to find the invoice) or resend_invoice_email, and no preconditions or exclusions.

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