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

Annotations already establish read-only, non-destructive behavior. The description adds genuinely useful behavior beyond that: the output is random and each line follows the exact EuroMillions format. It doesn't discuss duplicate handling or error behavior, but for a simple generator with an output schema this is sufficient.

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?

Two tight sentences that lead with the core action and immediately give the format constraints; the source URL is a minor but non-intrusive addition. There is no redundant restatement of the schema.

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 simple, stateless generator with one optional parameter, an output schema, and safety annotations, the description covers what the agent needs to invoke it. Nothing required for correct selection is missing.

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?

The schema fully documents the only parameter (lines: range, default, description), so the description carries no extra burden. The word 'lines' in the description corroborates the parameter but adds no new semantic information.

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?

Uses a specific verb ('generate') and resource ('random EuroMillions lines'), then pins down the exact composition (5 main numbers 1–50, 2 Lucky Stars 1–12), which separates it from generic siblings like hopi_lottery_number_generator.

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 usage context is implied: use it when random EuroMillions lines are needed. It does not explicitly contrast with alternatives (e.g. hopi_lottery_number_generator for generic lottery draws) or mention exclusions, so the guidance is adequate but not explicit.

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