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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description's enumeration of returned content is largely redundant with the existing output schema and adds no new behavioral context such as not-found handling or auth requirements.

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?

A single compact noun phrase with the resource front-loaded and no filler. It is efficient, though as a fragment it lacks the connective structure that would route an agent toward or away from it.

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 an output schema present, the return shape need not be explained, and annotations cover the safety profile, so the remaining gap is the lack of differentiation from search_invoices and no mention of error/not-found behavior. The definition is adequate but leaves a sibling-routing ambiguity unresolved.

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 'number' parameter is documented as accepting an invoice number with or without prefix. The description adds no syntax, format, or lookup-behavior detail beyond what the schema already provides, 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?

The description names the resource ('une facture') and enumerates what the detail contains (lignes, ventilation de la TVA, adresse de facturation, paiement), which is more specific than the title alone. It does not, however, contrast itself with the sibling search_invoices, so an agent must infer that this is the single-record lookup rather than a listing.

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?

There is no statement of when to use this tool versus search_invoices or report_unsupported_request. The only signal is the required 'number' parameter in the schema, so usage must be inferred entirely from structure rather than from the description.

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