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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuine value by disclosing the shape of the response (line items, taxes, totals, payments, remaining amount), but says nothing about behavior on an invalid or unknown invoice_id, or about data freshness.

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 front-loaded sentence with no filler, and the payload contents are readable at a glance. It is a noun fragment rather than a complete statement of the operation, which slightly reduces clarity for a first-time reader.

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 get-by-id read tool with annotations and full schema coverage, the description supplies the one thing the structured fields do not: what the returned invoice object includes. Missing only edge-case behavior, which is minor at this complexity.

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?

With a single parameter and 100% schema coverage — including a description that already says the id comes from bexio_list_invoices — the schema does the work. The description adds no meaning about the id beyond what is already structured, 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 identifies a single invoice and enumerates exactly what the payload contains (positions, taxes, totals, payments, remaining amount), which lets an agent distinguish it from the list-style siblings. It falls short of a full verb+resource statement and never explicitly contrasts itself with bexio_list_invoices or bexio_get_quote, relying on the name/title for the verb.

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: 'One invoice' signals single-record retrieval versus the listing tools, and the schema's reference to bexio_list_invoices hints at the discovery-then-fetch flow. There is no explicit when-to-use/when-not or named alternative in the description itself.

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