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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds genuine value by disclosing that the payload includes line items and a Veri*factu hash, which tells the agent what data it gets back. It does not cover behavior for a missing/invalid invoice_id or any auth constraints, which keeps it below a 5.

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 front-loaded sentence that identifies the resource and enumerates the notable returned fields with no filler. It is appropriately sized, though it spends its space on return contents rather than the parameter that an agent must supply.

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 usefully names the key return contents, and readOnlyHint covers safety. But for a lookup tool whose only parameter is undocumented, the description should at minimum explain what invoice_id is expected to be and possibly the error behavior for unknown IDs.

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% for the single required parameter invoice_id, an untyped-meaning integer with no explanation. The description mentions no parameter at all, so it fails to clarify whether this is an internal ID or the visible invoice number — a real ambiguity given the presence of get_invoice_display and series tools.

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 ('Get full details of a single invoice') with the scope made concrete by naming the returned content (line items, Veri*factu hash). It implicitly separates itself from list_invoices by saying 'single invoice', but never distinguishes itself from the other invoice-detail siblings such as get_invoice_display or get_invoice_facturae.

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: an agent can infer this is the single-invoice read versus list_invoices, but there is no explicit when-to-use, no mention of alternatives like get_invoice_display/get_invoice_facturae, and no stated prerequisites (e.g. whether the invoice must exist or be finalized).

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