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

Annotations already mark the tool as read-only (readOnlyHint=true). The description adds useful context beyond that: it notes the tool requires no account ('No requiere tener cuenta') and cites SELAE regulation as its source. This goes beyond the annotation's safety hint and provides operational context for the agent.

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 description is compact and front-loaded: it starts with the core purpose, then gives usage guidance, enumerates supported games, and ends with an account requirement. No filler. Every sentence earns its place, and the structure is logical for an agent to quickly extract the key facts.

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 read-only reference tool with no output schema, the description covers all necessary aspects: what it does, when to use, the supported games (which is a full enumeration), and the authentication constraint. Nothing an agent needs to correctly select and call this tool is missing, given its read-only nature.

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?

Input schema descriptions cover both parameters with 100% coverage, but the description adds significant value by enumerating the full list of valid values for the 'juego' parameter (Euromillones, La Primitiva, etc.), which the schema only hints at with examples. For 'tema', the description effectively repeats the schema description but the game list is a meaningful addition.

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 clear, specific statement of function: provides official game rules (reglas oficiales) covering cost, draw schedule, prize categories, and cashing. It explicitly enumerates the supported games, distinguishing it from sibling tools like resultado_sorteo (draw results) and comprobar_premio (prize checking). The scope is unambiguous and differentiated.

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 explicitly states when to use the tool: 'Úsala cuando pregunten cómo funciona un juego' (use when asked how a game works). It also lists the exact set of games it supports, which implicitly excludes other queries. However, it does not explicitly contrast with sibling tools, so it stops short of a full when-not/alternatives statement.

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