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

With no annotations, the description carries the full burden. It discloses token consumption (5-10k tokens) and the element/viewport distinction, which is useful. However, it does not mention other behavioral aspects like whether it is read-only, the return format, or potential failure modes. The token cost adds value but leaves some transparency gaps.

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 sentences with no fluff: the first fronts the verb and resource, second gives an alternative. Every sentence earns its place, and the token cost is a concise addition.

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?

Given 7 params, no output schema, and no annotations, the description provides clear purpose, usage guidance, and token estimates. It does not describe the return format, but the token count implies an encoded image and the schema covers parameters. The tool is simple enough that this is mostly complete.

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 description coverage is 100%, so the baseline is 3. The description adds the element-vs-viewport behavior, but this is already partly documented in the schema for id/selector ('Omit both for viewport screenshot'). No additional parameter meaning is provided beyond the schema.

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 primary action ('Capture element image') and the alternative scenario ('full viewport when no id/selector is given'). It distinguishes itself from sibling tool analyzePage, which is specified for form data/validation, making the purpose 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 explicitly says when to use the tool ('Capture element image, or full viewport when no id/selector is given') and provides a direct alternative: 'Use analyzePage for form data/validation.' This is a clear when-to-use vs. alternative guidance, similar to the top-calibration example.

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