analyze_screen

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

Annotations already declare readOnlyHint=true, so the description correctly aligns with a read-only operation. It adds valuable behavioral context: 'No external API key required' and 'DPI-aware coordinate mapping' for click interactions. This goes beyond the annotation and informs the agent about key characteristics.

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 concise sentences. The first sentence states the primary action and return value. The second adds two distinct benefits. No redundant or extraneous information. The structure is front-loaded with the most critical 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?

For a simple tool with one required parameter, readOnly annotations, and no output schema, the description covers the core functionality and key features (DPI mapping, no API key). It does not specify the return format or error handling, but given the context, these are minor omissions. The description is sufficiently complete for an agent to understand when and how to use the tool.

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 schema description for 'prompt' is generic ('Question or instruction about the screenshot'). The tool description enriches it by explaining that for coordinate queries, 'the agent will return DPI-corrected screen coordinates'. This adds specific meaning, helping the agent understand how to use the parameter effectively.

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 action ('Take a screenshot and return it') and the purpose ('for visual analysis'). It distinguishes itself from siblings like 'find_by_vision' by emphasizing that the agent performs the analysis, not the tool. The mention of 'no external API key required' further differentiates it from similar tools.

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 use for visual analysis but does not explicitly state when to use this tool versus alternatives (e.g., 'find_by_vision' for element detection or 'start_recording_screen' for video). No guidance on when not to use it or prerequisites are provided.

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