Capture viewport screenshot

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

The description discloses two behavioral traits: only Viewport mode supported and potentially slow response requiring a longer timeout. However, it lacks details on error handling, file storage, or overwrite behavior, which would be expected given no annotations.

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 concise at two sentences, front-loads the primary action, and adds necessary constraints and performance notes without extraneous information.

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?

The description covers the core functionality and key constraints, but lacks details about output (e.g., file path/name) and error scenarios. Given the tool's simplicity, this is adequate but not fully comprehensive.

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 input schema has no parameters, so no additional parameter documentation is needed. The description provides useful context beyond the schema, such as the RPC call and timeout hint, meeting the baseline for zero-parameter tools.

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 clearly states the tool captures a viewport screenshot and saves it as a file, using a specific RPC and capture type. No sibling tool performs screenshotting, so it effectively distinguishes itself.

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?

The description implies usage for viewport screenshots and notes a mode limitation, but does not explicitly state when to use this tool versus alternatives or when not to use it.

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