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

readOnlyHint=true already tells the agent this is a safe read, and the description adds genuinely new context: the checksum is retained for 3 months and the call exists to guarantee idempotency (avoid duplicate creation). It does not say what happens if the checksum is unknown or the window has expired, which is the remaining behavioral gap for an error-prone recovery path.

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?

One front-loaded sentence carrying trigger, action, rationale, and retention, followed by the endpoint path. Every clause earns its place and no sentence is wasted.

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 one parameter, full schema coverage, no output schema, and a readOnly annotation, the description is nearly self-sufficient — it even signals that the return value is the original request's reply. Only the failure mode (checksum not found/expired) is left undefined.

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 parameter is fully documented as 'The checksum given to superfaktura_create_invoice.' The description reinforces the same meaning but adds no format or provenance detail beyond the schema, so the baseline 3 applies.

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+resource ('fetch the reply of the ORIGINAL request by the checksum') and explains the scope ('of a create', tied to superfaktura_create_invoice). It is unmistakable against siblings like superfaktura_get_invoice or superfaktura_list_invoices, which retrieve documents rather than a prior request's response.

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 trigger condition is given: 'If a superfaktura_create_invoice call timed out, fetch the reply of the ORIGINAL request ... so the document is not created twice.' This names the sibling it complements and the exact situation that selects it, leaving nothing to inference.

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