capture_screen

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

With no annotations, the description carries the full burden. It usefully discloses the return channel (inline PNG) and the conditional side effect of save_path, but says nothing about device/serial targeting, failure behavior when no device is connected, latency, or whether capture is safe/non-destructive.

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 short sentences with the core action and return value front-loaded, then the optional side effect, then the intended use case. No filler and nothing buried.

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 two-parameter tool with no output schema and no annotations, the description covers the important output channel and the save_path side effect, which is genuinely helpful. It is still incomplete on the serial parameter and on error/no-device behavior.

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 0%, so the description must compensate for both parameters. It explains save_path well ('also writes the PNG there'), but serial is never mentioned, leaving an agent to guess its meaning and default behavior.

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 names a specific verb and resource ('Capture a screenshot') and adds the return format ('inline PNG image'), which implicitly separates it from capture_screen_to_file and capture_screen_base64. It stops short of naming those siblings explicitly, so an agent must still infer which capture variant to pick.

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 gives a usage context ('Ideal for an observe->decide->tap loop / OCR'), which is more than nothing. However, it never states when NOT to use it or points to the closest alternatives (capture_screen_to_file, capture_screen_base64), so routing between the three capture tools is left to inference.

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