Capture at breakpoints

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

With no annotations provided, the description carries the disclosure burden and does well: it explains the tool loads pages, checks multiple viewports, reports overflow, returns text, and warns that screenshots are costly. It does not mention default viewport behavior or exact output formatting, but it discloses the most relevant operational traits.

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 concise sentences. The first sentence front-loads the core purpose and expected output, and the second sentence delivers cost-aware guidance for a specific parameter. Every clause adds useful information without redundancy.

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 tool with three parameters and no output schema, the description covers the main behavior, return type, and parameter nuance. It leaves a minor gap by not specifying what happens when the optional viewports parameter is omitted, but an agent can still use the tool effectively with the provided information.

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 documents all three parameters at 100% coverage, so the baseline is 3. The description adds valuable meaning on top by warning that screenshots are expensive and should only be requested when genuinely needed, which helps agents avoid unnecessary resource use. The url and viewports parameters do not need additional explanation because the schema already covers them.

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 action: load a page at multiple viewport widths, check for sideways overflow, and name the single responsible element. It clearly distinguishes this tool from a generic 'capture' by explaining the analysis it performs and the text result it returns.

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 and practical guidance for the screenshots parameter, saying to pass screenshots:true only when an image is genuinely needed because each image is expensive. It does not explicitly compare to the sibling tool 'diagnose', but the intended use case is well implied.

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