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

Annotations already declare this a read-only, idempotent, non-destructive, closed-world operation, so the safety profile is covered. The description adds genuine behavioral context beyond that: the exact return fields, the 'uncertain' semantics for edge cases requiring a tax adviser, and the boundary that activity-level exemptions are out of 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?

The purpose is front-loaded in the first sentence, followed by tightly packed decision rules and a Returns summary. It is dense but nearly every clause carries a decision rule; the parenthetical enumerations are long yet functional rather than 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?

With no output schema, the description compensates by naming the return fields (evidenced, explanation, note, sources, guide url) and defining the 'uncertain' outcome. Combined with the classification rules and the explicit exemption boundary, an agent has everything needed to invoke and interpret the result.

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 baseline would be 3, but the description goes further by explaining the classification meaning behind the enum values (which instruments count as evidenced vs. which are 'not a payment'), and clarifies that in_person means 'during personal contact or at the premises'. This adds meaning the enum list alone does not convey.

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 precise verb (decide/classify) and resource (whether a payment is an evidenced sale under EET 2.0), and names the domain term 'kontaktní platba'. It is clearly distinguishable from siblings like eet_calculate_eet_off or eet_get_facts, which handle calculation and fact lookup rather than classification.

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?

Provides explicit decision conditions: in-person/premises payments are evidenced, gift-voucher redemption and remote payments (bank transfer, gateway, QR on invoice) are not, and 'uncertain' covers bank transfer on site and cash on delivery. It also routes away the exemption case ('not evaluated here – see eet_get_facts topic exemptions'), though it does not otherwise compare against sibling tools.

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