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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile needs no restating. The description adds real value by enumerating the returned payload (items, customer, payment methods, custom fields, status, dates, calculations), but says nothing about behavior on an invalid or missing ID or about response size.

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 short sentences, front-loaded with the core action and scope, and the return-content list is informative rather than padded. The enumerated field list is slightly long but each item signals a real part of 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 correctly takes on the burden of describing what comes back, and it does so at a useful granularity. What remains unstated is error behavior for a bad ID and whether any auth or scope is required, though annotations cover the read safety profile.

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?

Only one parameter, and the schema already describes it at 100% coverage, including its origin ('from list_invoices'). The description restates 'by ID' without adding format, source, or validation detail beyond the schema, 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 and resource ('Fetch full details of a single invoice by ID') and scopes it to one record, which separates it from the list-oriented sibling list_invoices referenced in the schema. It does not explicitly distinguish itself from single-invoice siblings like get_invoice_pdf_url or get_invoice_aging, so it falls short of a 5.

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?

Gives concrete when-to-use guidance: before an update to get current state, or when the user asks about a specific invoice's details. The read-before-write framing is genuinely useful for routing, but no when-not-to-use or explicit alternative is named.

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