screenshot_by_uid

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

Annotations indicate readOnlyHint=true, and the description adds the crucial behavioral detail that the output is base64 PNG. This complements the annotation by specifying the return format, which is beyond what the annotation provides. No contradictions found.

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 a concise single sentence that fully conveys the tool's purpose and output format. There is no redundancy or unnecessary detail, making it highly scannable for an agent.

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 two well-documented parameters and a read-only annotation, the description plus schema provide sufficient context. The return format (base64 PNG) is stated, and the saveTo behavior is explained in the parameter schema. Slight gap: the description does not define the exact response structure, but that's minor for a screenshot function.

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 already provides complete descriptions for both parameters (uid and saveTo), achieving 100% coverage. The outer description adds no additional parameter semantics, so it relies on the schema as expected.

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 (Capture), the target (element screenshot by UID), and the output format (base64 PNG). It distinguishes from sibling screenshot_page by specifying 'element' and 'by UID', making the tool's unique scope unambiguous.

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 the tool is for element-level screenshots, but it does not explicitly state when to prefer this over screenshot_page or other alternatives. There are no explicit exclusions or references to sibling tools, leaving usage context partially implied.

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