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

Annotations already establish readOnly, non-destructive, non-open-world behavior. The description adds context annotations cannot: the game runs entirely in the widget and generates no content, plus the in-game mechanics (snake grows, speed increases with score) — a useful cue for what happens after invocation.

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 short sentences, front-loaded with purpose and followed by gameplay context, then options, then the widget caveat. The options list slightly duplicates the schema but a reader scanning the description benefits from it.

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 zero-required-parameter, no-output-schema leisure tool the description covers everything needed to invoke it: what starts, what knobs exist, and that nothing external is generated. Only the post-invocation experience (a widget appears with no return payload) is left slightly implicit.

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% and the description only restates the four options, their enums (easy/medium/hard, classic/timed) and ranges (10-30, 1-10) that the schema already documents in more detail, including defaults. Baseline 3 applies since the schema does the heavy lifting.

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 ('Start a game of Snake') and the framing ('short study break') makes it instantly distinguishable from play_chess and play_memory_game. It doesn't explicitly contrast with those siblings, but the named game is unique enough that no ambiguity remains.

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?

'as a short study break' implies the context (leisure between study tasks) but gives no explicit when-not conditions and never names an alternative such as play_chess or play_memory_game. Adequate implied guidance, not routing guidance.

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