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

With only destructiveHint=true in the annotations, the description carries meaningful extra context: it takes the next number, is limited to one reversal per invoice, is irreversible, and may be transmitted to e-Factura/ANAF. These are exactly the mutation side-effects an agent needs before invoking a destructive operation.

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?

Three dense sentences plus the endpoint, front-loaded with the action and its irreversible consequences. Every clause earns its place; nothing is padded.

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?

For a 3-parameter mutation with no output schema, the description covers irreversibility, once-only semantics, and transmission behavior. Return/response details are not described, but no output schema exists to relieve that, so it is nearly complete rather than fully so.

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 three parameters are already documented, including issue_date's default and date constraint. The description reiterates the required series/number validation but adds no syntax or format beyond the schema, making the baseline 3 appropriate.

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?

The description gives a specific verb and resource: 'ISSUE a storno (credit) invoice that reverses an issued invoice.' That is far more precise than the name alone. It does not, however, explicitly distinguish itself from close siblings like smartbill_cancel_invoice or smartbill_restore_invoice, leaving the agent to infer the difference.

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?

It supplies concrete usage conditions: an invoice can be reversed only once, the storno cannot be undone, and it may be sent to e-Factura/ANAF. It also gives an operational instruction ('Confirm the exact series and number with the user first'). It stops short of naming when to prefer this over cancel/restore alternatives.

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