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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds genuinely useful context beyond them: the link is short-lived, the PDF carries e-conomic's own layout, and it requires a Cotlet API key with access to this app. The only gap is that it doesn't say what happens if the invoice isn't booked or the link expires.

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?

Front-loaded and reasonably tight, but the first two sentences restate the same fact ('download link for the PDF' / 'Returns the PDF as a download link'), which is mildly redundant. Every other sentence earns its place (short-lived link, layout, auth).

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 single-parameter read tool with no output schema, the description covers the important return behavior (a temporary download link rather than raw bytes), the layout provenance, and the auth prerequisite. Complete enough to call correctly, missing only edge-case behavior.

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 100% and the schema itself documents the single parameter ('Booked invoice number from list_unpaid_invoices'). The description adds no syntax or format detail beyond the schema, so the baseline 3 applies with the schema doing the heavy lifting.

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 ('Download link for the PDF of a booked invoice') and distinguishes itself from sibling invoice tools by being the PDF-retrieval operation specifically. An agent can tell this apart from get_invoice or list_unpaid_invoices without opening a 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?

Usage is implied by 'booked invoice' (i.e., an already-issued invoice) and the parameter note pointing to list_unpaid_invoices as the source of the number. However, there is no explicit when-to-use vs alternative guidance and no statement of when this tool is not appropriate (e.g., draft invoices).

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