aua_screen_frame

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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, openWorldHint=false), so credit here goes to added behavioral detail: 'cached' signals the frame is not freshly captured (and may be stale), and 'app-only' scopes it to the app rather than the full screen. That is meaningful disclosure beyond the annotations, though staleness/freshness semantics could be spelled out more explicitly.

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?

Two short fragments, zero padding, with the resource and the exclusion front-loaded. It is efficient, though the extreme terseness borders on under-specification rather than disciplined brevity.

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?

There is no output schema, so the description should explain the return value (image payload, format, resource reference) but does not, and the one parameter is left undefined in both schema and description. For a simple read-only tool this is a notable gap, not a fatal one.

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?

The sole parameter 'after_seq' has 0% schema description coverage and the description does not mention it at all. With low coverage the description must compensate for the gap, but it supplies no meaning for the parameter (sequence semantics, cursor behavior, or what happens when omitted).

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 fragment 'App-only cached video frame' identifies the resource (a video frame) and its scope (app-only), but omits a verb and never says it returns/retrieves image data. The second sentence distinguishes it from screenshot and UI-tree tools, which helps, but the core action remains implied rather than stated.

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?

Negative guidance ('Does not query UI trees or capture screenshots') implicitly steers an agent away from this tool when it needs a UI tree or a fresh screenshot, which is real value. However, it never names an alternative sibling (e.g., aua_screen, aua_observe) or states positively when this tool is the right choice over them, leaving usage for inference.

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