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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add context – and it does: it distinguishes 'announced by the shop' from 'estimated from its past rhythm,' warns that estimates are not guarantees, and notes that results are in German. It does not describe the result shape or what happens for an unknown shop name, which keeps it below a 5.

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?

Roughly four sentences, front-loaded with the core purpose, then the two mode branches, then the two caveats. The telegraphic 'With a shop:' / 'Without a shop:' fragments are efficient rather than sloppy, and every sentence carries information an agent would otherwise have to guess.

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 only two parameters, no output schema, and rich annotations, the definition is nearly complete: it explains both input modes, characterizes the returned data (announced vs. estimated promotions), and flags output language. The only gap is that, without an output schema, it doesn't say how the 'buy now or wait' verdict itself is expressed.

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 genuine meaning beyond the schema by explaining that the optional 'shop' parameter changes the entire output mode – a single shop's current and next promotion versus a country-wide list across shops. The country parameter's enum is fully documented in the schema and needs no repetition.

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 opens with a specific verb and resource: 'Tells whether a promotion is expected soon,' and then splits the behavior into two concrete modes (with a shop vs. without a shop). It never names the sibling tools (find_shop_vouchers, top_vouchers), so an agent must still infer that for current vouchers rather than future promotions those siblings are the right call.

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 conditions are given: 'when the user asks whether to buy now or wait, or when a shop will have its next sale.' That covers the primary use context well, but there are no exclusions or named alternatives telling the agent when to prefer find_shop_vouchers or top_vouchers instead.

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