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

Annotations only give readOnlyHint=false, openWorldHint=true, destructiveHint=false. The description goes well beyond them: it discloses the observable side effect (cost appears in Wydatki, Lista wydatków), which invoice types are rejected, the default per-call confirmation, the 'reaches other people' caution, and the required Cotlet API key scope.

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?

Purpose is front-loaded and every sentence carries real information (semantics, side effect, confirmation, auth). It is somewhat dense and mixes several concerns, but nothing is truly redundant.

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 one-parameter mutation with no output schema, the description covers everything an agent needs: what booking means, which inputs are valid, where the effect lands, the confirmation requirement, and the auth prerequisite.

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 there is a single parameter, so the schema already documents ksef_number. The description only restates that the number comes from list_ksef_purchase_invoices, adding no new syntax or format detail. 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?

States a specific verb and resource: 'Book a purchase invoice from KSeF as a cost'. It even disambiguates the Polish term 'Zaksięguj' and names the sibling list_ksef_purchase_invoices as the source, so an agent can distinguish it from the list/get tools.

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 says which document to feed in (from list_ksef_purchase_invoices) and constrains applicability: VAT and corrective invoices work, advance/final invoices are booked in an order and refused. It doesn't name an explicit alternative booking path, but no obvious sibling competes for this action.

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