screencast

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

Annotations already declare readOnlyHint=true, and the description does not contradict that. It adds valuable behavioral context beyond the annotation: it uses the xdg portal to org.gnome.Mutter.ScreenCast, skips the consent dialog, encodes on the iGPU, and suggests reading frames back with ffmpeg. This is useful implementation-level transparency.

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?

The description is compact and front-loaded: purpose first, then the key usage decision, then brief implementation detail, then the outcome-readback hint. No sentence is redundant, and the structure makes the most decision-relevant information appear early.

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 screen-recording tool with no output schema, the description sufficiently covers what the output is (h264 mp4), how to consume it (ffmpeg), and the key behavior (no consent dialog, iGPU encoding). It does not detail return values or consequences of optional parameters, but those are secondary and partly covered by the input schema defaults.

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 only 40%, with fps, seconds, and include_cursor lacking schema descriptions. The tool description mentions screen vs. one window, which relates to target, but does not explain the semantics of fps, seconds, or include_cursor. With low schema coverage, the description needed to compensate for those parameters but did not.

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 starts with a specific verb and resource: 'Record the screen, or one window, to an h264 mp4.' It clearly differentiates itself from screenshot by stating when motion capture is needed, naming the sibling tool explicitly and explaining why stills are insufficient.

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 explicitly says to use this tool 'instead of screenshot whenever the thing being judged MOVES' and gives concrete examples: animation, transition, scroll, stutter, hover state. It also explains the limitation of the alternative ('Stills cannot show motion and bursting them tops out near 5 fps'), so an agent can choose confidently.

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