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

The description discloses read-only behavior, consistent with readOnlyHint, and adds critical behavioral context: amounts and currency come directly from Xero and must not be converted or assumed to match Invio. This goes beyond the annotation and helps prevent incorrect downstream usage.

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 with no filler. The primary purpose is front-loaded, and the critical ID-source constraint and currency warning are stated efficiently.

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 simple single-invoice retrieval tool with no output schema, the description covers the essential return content (full detail, line items) and provides necessary cautions. It is complete enough for an agent to use correctly, though it doesn't describe the exact response structure.

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?

The schema describes the organisation parameter but not invoiceId. The description compensates by explaining that invoiceId must be a Xero InvoiceID (GUID) from list_xero_invoices, adding meaning beyond the format field. This addresses the key parameter semantic gap.

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 clearly states the tool returns full detail on one Xero invoice, including line items. It distinguishes itself from list_xero_invoices by specifying single-invoice scope and from other get tools by the resource type.

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?

It explicitly instructs that invoiceId must be a Xero InvoiceID from list_xero_invoices, not an Invio ID, which guides correct usage. It implies using this tool when full detail on one invoice is needed, though it doesn't explicitly contrast with sibling tools or state when not to use it.

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