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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the bar is lower, and the description still adds two non-obvious behaviors: set is a partial merge where omitted fields are preserved, and nextNumber is monotonic ('only moves forward'). What it omits is any statement about what 'get' returns or how numbering interacts with existing invoices.

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 compact sentences: the resource scope first, then the action model and the two behavioral rules in parentheses. No filler, and the most decision-relevant constraints are packed into the trailing clause.

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 14 parameters, no output schema, and thin schema descriptions, an agent still cannot tell what 'get' returns or how most fields behave (required formats, currency codes, whether empty string clears a field). The mutation semantics are well covered; the read-side and per-field details are not.

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 only 21% across 14 parameters, so the description carries a real burden. It partially compensates by grouping the parameters into business details, payment instructions, and numbering, and by explaining the semantics of nextNumber and omitted fields — but the majority of parameters (currency, terms, address, prefix/padding) get no additional meaning beyond their names.

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 the resource (invoice settings) and enumerates the content domains it governs — business details on invoices/receipts, payment instructions, numbering — plus the two supported actions (get/set). It reads clearly as a settings singleton, distinct from invoices_manage and invoices_list, although it never names those siblings explicitly.

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 get/set pair is stated and the partial-update rule ('omitted fields unchanged') tells the agent how to call a set, but there is no guidance on when to reach for this versus invoices_manage or sending_settings. Usage is implied by the action enum rather than explained.

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