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

Annotations only declare readOnly=false, destructive=false, openWorld=true. The description goes well beyond them: auto-numbering when no number is supplied, what is returned (ID, totals, e-invoice status), that the due date becomes the payment due date, that no SDI transmission occurs, the per-call confirmation requirement, and the Cotlet API key/access requirement. No contradiction with the write-capable, non-destructive annotation profile.

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 key behavior; the SDI/send_einvoice caveat and the confirmation/auth notes each carry distinct value. Only minor redundancy in restating the invoice inputs ('lines, VAT and a due date') that the schema already lists.

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 mutation tool with no output schema and 100% schema coverage, the description fills the remaining gaps: it summarizes the return payload (ID, totals, e-invoice status), notes side effects (auto-numbering, no SDI send), and covers the confirmation and auth prerequisites.

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 baseline is 3, but the description adds real meaning for due_date (it becomes the payment due date) and for totals (net, VAT, gross). It is slightly muddled by referencing an auto-numbering behavior for a 'number' that does not appear among the 7 schema properties.

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+resource ('Create an invoice for a client, with lines, VAT and a due date') and immediately distinguishes scope from the sibling that actually sends it ('use send_einvoice for that'). An agent can separate this from get_invoice/list_invoices/send_einvoice without opening any schema.

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 names the alternative and the condition that selects it ('Creating the invoice does not send it to SDI; use send_einvoice for that'), and adds the confirmation policy ('By default you confirm each call; you can switch that off for this tool'). When/when-not routing is spelled out rather than inferred.

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