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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true; the description adds useful confirmation that nothing is persisted or transmitted and notes the two possible outcome classes (validation result vs. A-Cube's errors). It stops short of saying whether validation is purely local/remote or what an error payload looks like, but it discharges the behavioral burden well for a read-only tool.

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 carrying the action, the side-effect guarantee, and the return classes, plus a short endpoint tag. No filler.

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?

For a read-only validation tool with a fully described two-parameter schema and no output schema, the description covers the important ground. The remaining gap is that the "validation result" return shape is not characterized at all (valid/invalid flag vs. list of rule violations), which matters since no output schema exists to fill that in.

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 100%, so the two parameters (including the nested FatturaPA body and header structures) are already well documented in the schema. The description adds nothing about parameters, 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?

Specific verb + resource ("Checks an invoice against the FatturaPA rules") with an explicit non-effect clause ("without creating or sending anything") that separates it from acube_create_draft_invoice and acube_send_draft_invoice. The endpoint reference (POST /invoices/validate) reinforces the read-only validation scope.

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?

The "without creating or sending anything" phrasing implies this is a pre-flight check rather than a substitute for creating or sending, so usage is inferable. But there is no explicit when-to-use guidance naming acube_create_draft_invoice or acube_send_draft_invoice as the follow-up steps, and no statement of prerequisites (e.g. what a "missing field" result means for the next call).

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