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

Beyond the read-only annotations, the description discloses the auth requirement ('Needs the user's Cotlet API key with access to this app'), the ordering of linked reminders ('listed oldest first'), and clarifies provenance of computed totals. These are exactly the behavioral traits annotations do not carry, so the description adds real value.

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?

The opening is front-loaded, but the definition is repetitive: the first sentence and 'Returns one invoice as the invoice mask shows it...' both enumerate positions, totals and status. Consolidating those would remove roughly a third of the text without losing meaning.

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 no output schema, the description carries the return-value burden and does so by enumerating customer, positions, totals, status, e-invoice toggle and reminders. Annotations already cover the safety profile, so the only meaningful gap is error behavior (e.g., an unknown invoice_id).

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 description coverage is 100% and the single invoice_id parameter is documented in the schema as coming from list_invoices. The description adds no format, syntax, or constraint detail beyond what the schema already provides, so the baseline of 3 is correct.

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 states a specific verb and resource ('One invoice with its positions, totals, status...') and makes clear it returns a single invoice rather than a list, implicitly separating it from sevdesk_list_invoices. It is clear and concrete, but never names or contrasts a sibling tool explicitly, which is what separates a 5 from a 4.

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?

There is no explicit when-to-use or when-not-to-use guidance, and no alternative is mentioned. The phrase 'so your agent can see whether a customer was already chased' hints at a use case (checking reminder status) but does not tell the agent when to select this tool over sevdesk_list_invoices or sevdesk_create_payment_reminder.

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