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

Goes well beyond readOnlyHint=true: it describes the unavailable/available=false row state with unavailable_reason, explains what last_number means when numbers were skipped, and warns that any argument is refused with VALIDATION_ERROR. These are behaviors an agent cannot infer from the schema.

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?

Front-loaded with purpose and no filler sentences, but the field list and the parenthetical about next year's form create a dense single-paragraph block that is harder to scan than it needs to be.

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?

No output schema exists, yet the description effectively documents the return row (prefix, last_number, next_number, next_preview) plus the availability fields. Combined with the empty input schema and readOnly annotation, nothing needed to call this correctly is 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?

Zero-parameter tool, so baseline is 4; the description exceeds that by stating explicitly that it takes no arguments and how stray arguments fail (VALIDATION_ERROR), matching the empty schema with additionalProperties=false.

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 resource ('how each numbered document type counts') and enumerates the exact row shape: prefix, last_number, next_number, next_preview. It also names the sibling tools it is not (sales_settings_numbering_set, sales_settings_upsert), so an agent can separate read from write immediately.

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?

Explicit routing rules: use sales_settings_numbering_set to change a next number or a credit-note/debit-note/receipt prefix, and sales_settings_upsert for invoice and quote prefixes. Adds an operational rule ('Copy next_preview, never build it') that prevents a common misuse.

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