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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds value by disclosing the returned fields (totals, balances, status, dates) and that comments are optional, but says nothing about error behavior for an unknown id, permissions, or rate limits.

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 sentence with the key qualifier ('by id') front-loaded, closed by the endpoint path. The middle becomes a field-list dump, but every item conveys return-shape information that would otherwise be missing without an output schema.

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 no output schema, the description carries the return-shape burden and does so well by enumerating the document contents and optional comments. The remaining gap is failure/error behavior and confirmation of what the endpoint returns when the id does not exist.

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%, so invoice_id, language and include_comments are fully documented in the schema itself. The description only glancingly hints at include_comments via 'Optionally with its comments' and adds nothing about the language parameter, so 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?

Names the resource (invoice document) and the access mode (single document by id) and enumerates the returned content, so it is distinguishable from invbg_list_invoices. It never explicitly names the list sibling as the alternative for multi-document reads, so it stops short of a 5.

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: fetch one document when you already have its id. There is no explicit when-to-use/when-not or pointer to the list tool in the description text (the useful 'id from invbg_list_invoices, not the printed number' note lives in the schema instead).

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