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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds real value by disclosing what the response contains (line items and payments) and the underlying GET endpoint. It does not cover not-found behavior or auth requirements, which keeps it at a moderate level.

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?

Two short sentences: the payload first, the endpoint second. Nothing is wasted and the most decision-relevant information (full detail with line items and payments) is front-loaded.

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 compensates by naming the returned components. For a single-parameter read tool that is nearly enough; only error/empty-result behavior is left unstated.

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 single invoice_id parameter is fully typed with bounds, so the schema carries the burden. The description only echoes the path variable via 'GET /invoices/{id}' and adds no format or sourcing guidance beyond that, making baseline 3 appropriate.

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?

The description names the resource (a single invoice) and its scope explicitly: 'in full with its line items and payments.' That distinguishes it from the sibling splose_list_invoices without naming it. It stops short of a clean verb-first phrasing, but the operation is unambiguous.

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: 'One invoice' plus the enriched payload suggests this is the detail-view counterpart to splose_list_invoices. There is no explicit routing guidance (e.g., 'list invoices first to obtain the id') and no stated preconditions, so the agent must infer when to call it.

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