Capture visible screenshot

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It explicitly states that the tool only captures the visible tab viewport and that iframe frameViewport bounds are invalid, which are key behavioral traits. It also mentions cropping options. While it does not state permissions or side effects, for a screenshot tool these are less critical. The description adds meaningful context beyond the schema.

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 three sentences, each with a clear purpose: the core action, a critical constraint, and cropping options. It is front-loaded with the main purpose and avoids redundancy. Every sentence earns its place, making it highly efficient and easy to parse.

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 the tool has 6 parameters, a nested object, and no output schema, the description covers the main behavior, the iframe limitation, and the cropping options. It does not explicitly state the output format, but that is implied by the tool name and the schema. It also does not mention what happens when no ref or bounds are provided, but 'Capture the visible tab viewport' implies a full viewport capture. The description is sufficient for an agent to call the tool correctly in most scenarios.

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 83%, so most parameters are already documented. The description adds value by clarifying the semantics of ref and bounds: 'top-document snapshot ref' and 'tabViewport bounds' explain the coordinate system and cropping targets. It also reinforces the mutual exclusivity of ref and bounds by presenting them as alternatives. This goes beyond the schema's terse descriptions.

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 and resource: 'Capture the visible tab viewport.' It also includes a scoping constraint ('tab-target only') and a caveat about iframe coordinates, which clearly distinguishes it from potential sibling tools that handle full-page or iframe captures. This is not a tautology and provides a precise purpose.

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 gives clear context for when to use the tool: it is tab-target only and iframe frameViewport bounds are not valid crop coordinates. This implicitly tells the agent not to use it for iframe captures, and it suggests using it with a top-document snapshot ref or tabViewport bounds for cropping. However, it does not explicitly name alternative tools like snapshot or visible_snapshot, so the guidance is strong but not exhaustive.

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