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

Goes well beyond the annotations: it discloses asynchronous behavior ('returns immediately with build progress'), a daily free allowance quota, an OAuth sign-in / handoff URL fallback path, and explicit safety guarantees ('never charges anyone or sends messages'). This is the kind of operational detail annotations cannot express.

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?

Four tightly packed sentences with the core action front-loaded and no filler. The quota/OAuth details are relevant but slightly interrupt the primary purpose statement; overall still efficient.

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 does the work of explaining the return (immediate build-progress response, plus OAuth request or handoff URL on exhaustion). For a fire-and-forget async generator this is nearly sufficient, though it could say more about how progress is polled (e.g., via get_made_game).

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 description coverage is 100%, so all four parameters are already documented, including the 64-hex idempotency key and the brief contents. The description echoes the brief's role ('sender's supplied habits or inside jokes') but adds no format or constraint detail beyond the schema, so the baseline 3 applies.

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 verb and resource: 'Starts generation of a small browser game about one person.' The scope (one recipient, derived from supplied habits/inside jokes) is concrete. However, it never distinguishes itself from siblings like create_custom_game, revise_custom_game, or get_made_game, so the agent must infer the boundary.

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?

Implicit usage context is present (quota-limited free generation, OAuth handoff when allowance is exhausted), but there is no explicit 'use this when X, use create_custom_game instead when Y' guidance despite four closely related sibling tools. The agent is left to infer the routing.

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