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

Goes well beyond readOnly/idempotent annotations: it explains host capability variance (MCP Apps player vs. new-tab fallback vs. plain-text play_url), the link_out outcome and its causes (listing-only, stale check, Mature, disallowed site), and names error codes. This is exactly the behavioral context an agent needs before claiming success.

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?

Front-loaded with the core action and keeps everything in a single dense paragraph with no filler. It is somewhat run-on given the number of fallback cases, but each clause carries operational information the agent needs.

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?

Covers the full decision surface: input forms, host capability differences, fallback link behavior, when not to assert playback, and error codes. Even though an output schema exists, the description's explanation of mode/link_out/reason is what makes the tool callable correctly across host environments.

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 coverage is 100%, and the schema descriptions already document the game_id forms and that query resolves to the top search_games hit. The description largely restates those semantics; its additional value is mainly outcome-related (link_out when only on the developer's site), not parameter-level detail. Baseline 3 is appropriate.

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 concrete verb and resource ('Play an ArcadeIndex game right inside the chat') and immediately distinguishes itself from retrieval siblings by describing what playback means here (embedded player vs. link out). An agent can tell this apart from get_game or search_games without opening a schema.

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?

Explicitly says to pass game_id (with accepted forms, including URLs from search_games, trending, games_like, new_games results) or query (top search hit is played). It also tells the agent what to do when playback isn't possible: give the user the link_out URL, and don't claim the game is running unless the user says so. That is unusually clear routing guidance.

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