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

Annotations already establish readOnlyHint, idempotentHint, and non-destructive behavior, and the description adds important caveats beyond them: it does not reserve the number, does not check whether the number is unused, and returns no suggestion when no numbered invoice exists. The return value's exact shape is not described, keeping this from 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?

Front-loads the core behavior, then gives a concise usage cue and a compact caveat. Every sentence carries distinct information with no repetition.

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?

Given a single optional parameter, full schema coverage, strong annotations, and no output schema, the description covers the mechanics, usage context, and key limitations. It could be slightly more complete by indicating the return type (e.g., a number string or null), but it is otherwise sufficient to call the tool correctly.

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 the schema already documents the single optional parameter and its omission behavior. The description adds meaning by specifying 'exact company name' for the recipient scope, which goes slightly beyond the schema wording.

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 ('suggests the next invoice number') and explains the exact mechanism: incrementing the trailing number of the latest numbered invoice. It also distinguishes the scoped and unscoped modes, so an agent can separate it from sibling tools like create_invoice or duplicate_invoice.

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?

Explicitly says to use it 'before creating or finalizing an invoice that needs a number,' which gives a clear trigger condition. It does not name a specific sibling alternative or exclusion, but the usage context is unambiguous.

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