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

The readOnlyHint annotation already covers the safety profile, so the description's added value is disclosing what is returned (status, totals, dates, client, payment terms) and, importantly, what is NOT returned (line items, which live in a sibling tool). It does not mention failure modes (e.g., unknown id), so it stops short of full behavioral disclosure.

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 short sentences, no filler, with the core purpose front-loaded and the line-item caveat placed immediately after so the reader learns the boundary before invoking.

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 correctly takes on the job of describing the return payload and the payload's boundary (no line items), and it points to the tool that supplies them. For a one-parameter read tool this leaves nothing an agent needs missing.

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% and the schema already explains that the id comes from billomat_list_invoices, so the structured field carries the full burden. The description adds no syntax or format detail for the id beyond that, which is the expected baseline when the schema is complete.

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+resource ('Get one invoice'), enumerates the returned fields (status, totals, dates, client, payment terms), and distinguishes itself from the list tool by scoping to 'one'. It even routes the related concern (line items) to the correct sibling, so an agent can separate it from billomat_list_invoices and billomat_list_invoice_items without opening a 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?

The single-record framing plus the explicit pointer that line items come from billomat_list_invoice_items clearly signals when this tool applies versus the list/items tools. However, it never explicitly names billomat_list_invoices as the way to obtain the id (that hint only lives in the schema), so usage guidance is strong but not fully self-contained.

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