Get Invoice

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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds meaningful behavior beyond them: url and pdfUrl require a signed-in user while downloadUrl works unauthenticated for only 15 minutes, amounts are normalized to cents, and an ID from another account yields INVOICE_NOT_FOUND. These are operational details an agent cannot derive from the schema or 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?

Three sentences, front-loaded with what the call returns, then the differing URL behaviors, then the ID source and error case. Dense but no filler; the field enumeration is long yet each item is load-bearing for understanding the payload.

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 must carry the return contract — and it does, naming the principal response fields, their units, and link lifetimes, plus auth requirements and the failure mode. The only material omission is differentiation from the get_invoice_pdf sibling.

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?

There is a single parameter with 100% schema description coverage, so the schema already carries its meaning; the description's cross-reference that IDs come from list_invoices reinforces the schema text rather than adding new semantics. Baseline for a fully documented small parameter set.

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?

Specific verb+resource ('Get one invoice as data') followed by an enumeration of exactly what comes back: bill-to, payment method with card brand/last four, line items with term and resulting domain expiry, and gross/refunded/net totals in cents. It also states the source of valid IDs ('Invoice IDs come from list_invoices'), which separates it from the list sibling.

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?

It gives the prerequisite for obtaining an invoice_id (list_invoices) and the error behavior for a foreign ID, plus practical guidance on which URL to hand a user. However, it never addresses the obvious alternative sibling get_invoice_pdf — an agent choosing between retrieving invoice data and fetching the PDF gets no explicit when-to-use/when-not guidance.

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