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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and closed-world scope, so the safety profile is covered. The description then adds genuinely useful disclosure the annotations don't provide — exactly what data comes back, including status enumeration values and payment breakdown — which matters because no output schema exists.

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?

It is front-loaded with 'Full invoice' and then a field list, but the bulk is one long run-on sentence with internal redundancy ('amount due' in the opening list repeated later as 'due', plus 'paid, credited and due'). It is dense rather than padded, yet the structure could be tightened into grouped clauses.

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 and no annotations covering return shape, the description's thorough enumeration of status, dates, totals and payment records is exactly the completeness an agent needs to decide whether this call answers its question. The only gap is the absence of guidance on when to choose this over list_invoices.

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 only one parameter and schema description coverage is 100%, with the schema itself saying 'Invoice ID from list_invoices.' The description adds no further meaning about invoice_id (no format, no cross-reference behavior on a bad ID), so the baseline 3 is appropriate when the schema carries the semantics.

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 opens with a specific verb-less but unambiguous statement — 'Full invoice' — and enumerates the exact contents, making it clear this is a single-invoice detail fetch keyed by ID. It never explicitly names list_invoices as the summary alternative, so sibling differentiation is only implied by the schema's 'Invoice ID from list_invoices' hint rather than stated in the description.

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: 'Full invoice' and the exhaustive field list suggest 'use this when you need complete invoice detail,' but there is no explicit when-to-use, when-not-to-use, or named alternative (e.g., list_invoices for summaries). An agent must infer the routing decision.

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