Responsive audit across all breakpoints

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It discloses that all four full-resolution renders are saved to one run directory, paths are reported, the previously active viewport is restored afterwards, and webp compression is applied. It also notes that sizeMode 'thumb' shrinks the over-the-wire image. This is strong behavioral transparency for a capture tool, though it doesn't detail failure modes or exact path format.

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 sentences, front-loads the core action, and every clause earns its place. It packs compression, sizeMode behavior, disk saving, path reporting, and viewport restoration into a compact, readable form. No filler or 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 4 parameters, 100% schema coverage, and no output schema, the description covers the key behavioral aspects an agent needs: what gets captured, how images are delivered, where they are saved, and side effects on viewport. It doesn't describe the exact output format of the reported paths, but the absence of an output schema makes that a minor gap. Overall, it is complete enough for correct invocation.

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 schema already documents all four parameters. The description adds value by explaining the relationship between sizeMode and the four-image turn affordability, and by clarifying that disk always gets full-resolution even when thumb is sent. This goes beyond the schema's per-parameter descriptions, so a 4 is warranted.

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 ('Capture'), a specific resource ('one URL at all four breakpoints'), and the key outcome ('in a single call'). It also distinguishes itself from sibling tools like capture_page_screenshot and find_breakpoints by emphasizing the multi-breakpoint matrix behavior. The title reinforces the purpose, and the description adds concrete detail about compression and saved renders.

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 when to use this tool: when you need a responsive audit across all breakpoints in one call, and it mentions the sizeMode option to keep the turn affordable. It doesn't explicitly name alternatives or exclusions, but the context signals and sibling list make the use case clear. A 4 is appropriate because it gives clear context without explicit when-not-to-use guidance.

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