React on the screen

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

With annotations only covering safety flags (readOnlyHint=false, destructiveHint=false), the description carries the behavioral burden and does add real context: the card auto-reverts to the resting face after a few seconds, and the name/team colour are pulled from the control panel (a cross-tool dependency). It also reveals a side effect on the lights, which overlaps with set_lights, but doesn't say whether this blocks, whether it fails if the robot is disconnected, or whether it overrides show_emoji/show_text.

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?

Three sentences, front-loaded with the core action and content, then use cases, then the auto-revert caveat. The enumerated game examples are slightly verbose but earn their place by mapping events to expressions. No filler or restated title.

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 3-optional-parameter, no-output-schema tool, the description covers what is displayed, where the name/colour come from, the default caption behaviour, and the auto-revert timing. Remaining gaps are error/precondition behaviour (robot connection) and interaction with the other display tools, but the essentials for correct invocation are present.

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 67% (hold_s and caption documented there; the expression enum has no per-value description). The description compensates by illustrating which expressions map to which game situations and by restating the revert behaviour ('goes back to the resting face after a few seconds') that gives hold_s meaning. It omits the 'focused' enum value present in the schema, a minor gap.

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 gives a concrete verb and resource ('Show the player card on the robot's screen') and enumerates exactly what the card contains: expression face, player name, team colour from the control panel, and lights in team colour. This composite nature implicitly distinguishes it from siblings like show_emoji, show_text, and set_lights, though it never names those alternatives explicitly.

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?

It provides concrete when-to-use context tied to game events ('excited after a goal, sad after a miss, wink after a good pass, surprised after a bump'), which tells the agent the intended scenarios. It stops short of explicit exclusions or naming the sibling tools (show_emoji/show_text) that an agent might otherwise pick, so no routing rule is stated.

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