Take a desktop screenshot

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds context beyond annotations by specifying it captures the Linux desktop as PNG image content, and that it reflects visible state. This is useful, though it could mention potential caveats like screen resolution or multi-monitor handling, but that is minor given the 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 two sentences: the first states purpose, the second gives usage guidance. It is front-loaded, efficient, and every sentence earns its place with no redundancy or fluff.

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 simple, zero-parameter tool with strong annotations, the description is complete. It covers what it does (capture desktop screenshot), the output format (PNG), the platform (Linux), and when to use it (before coordinate selection and after state changes). No critical information is missing.

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 tool has zero parameters, so schema coverage is 100% and there is nothing to explain. The baseline for zero parameters is 4, and the description adds clarity about the output format (PNG image content), which is relevant context even though not a parameter.

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 states a specific verb ('Capture') and resource ('current Linux desktop'), with a clear output format ('PNG image content'). It clearly distinguishes itself from sibling tools like click or type_text, which are input actions rather than observation.

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 provides explicit usage guidance: 'Use before choosing coordinates and again after every action that changes visible state.' This tells the agent exactly when to invoke this tool relative to other actions, which is highly actionable and context-rich.

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