See the frame the game is drawing

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

With readOnlyHint=true already covering the safety profile, the description adds substantial implementation context: it re-runs Graphics._app.render() and reads the canvas in the same task, which is why it works without preserveDrawingBuffer. It also discloses a known blind spot (DOM-based video is excluded) and the playtest dependency — all non-obvious traits not derivable from annotations or schema.

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?

Five tight sentences, front-loaded with the core action, then differentiation, then mechanism, then caveats. Every sentence adds information; nothing is restated from the title or schema.

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?

No output schema exists, but the description states the return artifact (a PNG of the composited frame), the mechanism, and the operational precondition, which is everything needed to call and interpret this tool correctly.

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?

Only one parameter (saveTo) at 100% schema description coverage, so the schema already defines its meaning and the description does not elaborate on it. Baseline 3 is appropriate when the schema carries the parameter explanation.

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+resource — 'Grab the running game's own composited frame as a PNG' — and enumerates exactly what is composited into it. It explicitly contrasts itself with the sibling render_map ('shows what the data says; this shows what the player sees'), so an agent can separate the two without opening either 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?

Names the alternative (render_map) and the condition that selects it, plus a hard precondition: 'Needs a running playtest.' It also carves out a scope exclusion (video playback is not part of the frame). It stops short of a full when/when-not matrix, but the routing signal is clear.

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