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

Annotations already declare readOnlyHint=true, destructiveHint=false and idempotentHint=false, so safety is covered. The description adds genuinely new behavior: the response carries a seed, and re-supplying that seed reproduces the identical draw ("that is how a draw is checked"), which is the key non-obvious trait given idempotentHint=false.

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 in the first clause, then the named-game list and the custom path follow logically. The game enumeration is long but earns its place because the schema only provides bare enum keys with no explanation of what each game means.

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 an 8-parameter tool with no required fields and no output schema, the description covers both invocation modes, the meaning of every enum, and the seed round-trip. What is missing is the concrete shape of the returned answer (how sets are grouped, field names) beyond the seed mention.

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?

With 88% schema coverage the baseline is 3, but the description goes further: it decodes each enum value (kr645 = Lotto 6/45 South Korea, etc.), spells out the min/max/count custom contract, and clarifies that extras are bonus balls drawn apart from 1 to extra_max. It also notes game may be omitted when count and max are given, a schema gap the schema itself does not state.

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 action (produce random numbers) on a specific resource (a named lottery game or custom format), which separates it from the retrieval siblings get_draw and check_ticket. It never explicitly names those siblings, so an agent must infer that this tool generates rather than looks up draws.

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?

The description thoroughly explains the two usage modes (named game vs game='custom' with count/max), which is real guidance, but it says nothing about when to reach for this tool versus get_draw or check_ticket, nor about prerequisites. Usage is implied rather than contrasted with alternatives.

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