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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuine context beyond that: it discloses the exact scope of returned data and, notably, that the linked invoice portion is deliberately limited ('IDs, number, status and document links only'), which prevents an agent from expecting a full invoice. It stops short of noting any paging or missing-record behavior, so not 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?

Two sentences, zero padding, and the highest-value information (what is returned, and the linked-invoice scope limit) is front-loaded before the sibling routing. Every clause earns its place.

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?

There is no output schema, so the description must explain return values — and it does so in detail, including the enum of possible statuses and the deliberate truncation of linked-invoice data. Combined with the annotations covering the read-only profile, an agent has everything needed to call this correctly.

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?

One parameter with 100% schema description coverage ('Credit note ID' plus a digits-only pattern), so the schema already carries the semantics. The description's 'by ID' adds nothing beyond it. Baseline 3 applies when the schema does the heavy lifting.

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 one credit note by ID') and enumerates exactly what comes back: status with its enum values, number, issue date, reason, lifecycle timestamps, document links, plus a bounded linked-invoice summary. An agent can distinguish this from every sibling get-*/list-* tool without opening the schema.

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?

Names three alternatives with the condition that selects each: preview-invoice for the full invoice, create-credit-note to draft, submit-credit-note to apply. It also implicitly rules out preview-invoice for a compact view. This is explicit when/when-not/alternative guidance.

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