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

readOnlyHint=true already establishes the safe-read profile, and the description adds genuinely useful context beyond it: the set of fields returned, the included lexwareAppUrl deep link, and the concrete HTTP route GET /v1/invoices/{id}. It does not mention error behavior for a missing/invalid id, so it stops short of a 5.

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 dense sentence front-loads the operation and then lists the payload fields with no filler; the endpoint is appended as a compact suffix. Every clause earns its place, though the trailing endpoint is arguably redundant with the tool name.

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 correctly compensates by enumerating the returned fields (status, line items, totals, tax, payment/shipping conditions, lexwareAppUrl). Nothing essential for invocation is missing, though it could note behavior 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?

There is one parameter and schema coverage is 100%, including the 'from lexware_list_vouchers' provenance note, so the schema already carries the semantics. The description's 'by id' adds nothing the schema does not.

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 and resource ('Get one invoice by id') and enumerates what the record contains (status, line items, totals, tax amounts, payment/shipping conditions, related vouchers), which cleanly separates it from sibling getters like lexware_get_credit_note or lexware_get_quotation. The endpoint path reinforces the operation.

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 lookup intent is clear and the sibling name-set makes the resource obvious, but there is no explicit when-to-use/when-not guidance or pointer to alternatives (e.g., lexware_get_payments or lexware_list_vouchers). Usage is implied rather than stated.

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