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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), so the description's 'without changing the invoice' is confirmatory. It adds genuinely new behavior context: the exact response shape and the state dependency that both links are null until the invoice is submitted and the document generated — a non-obvious empty-result condition.

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 the core action and constraint, then the return shape, then the sibling routing. No filler; every sentence carries information an agent needs.

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?

There is no output schema, but the description compensates by listing the returned fields and explaining the null-link state, so an agent knows exactly what to expect. Combined with the sibling routing and the 100%-covered id parameter, nothing needed to call this tool 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?

Schema description coverage is 100% for the single id parameter ('Invoice ID, as returned by list-invoices'), so the schema does the heavy lifting. The description adds no extra parameter syntax or edge cases (e.g., what happens with an unrecognized id), so the baseline 3 applies.

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 (get) and resource (invoice's generated document links) and immediately scopes it ('without changing the invoice'). It even enumerates the exact return fields, so an agent can distinguish it from preview-invoice and generate-invoice-pdf without opening any 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?

Explicitly routes alternatives: 'Use preview-invoice for the full invoice details, or generate-invoice-pdf to submit a draft and get its links.' It also states the precondition under which the tool is useful (links are null until the invoice is submitted and Classic has generated its document).

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