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

Goes well beyond the annotations: it discloses a daily browser-time budget/rate limit, that it returns screenshots, that it also loads with JavaScript off, and specifies the exact fallback path when the budget runs out. The readOnly/openWorld annotations cover safety, and the description layers operational constraints on top.

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?

Front-loaded with the core action and viewports, and the budget/fallback caveat is placed last where it belongs. It is dense — a long chain of clauses that could be bulleted — but nearly every clause conveys a distinct check, so little is wasted.

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 complex multi-viewport rendering tool, the description covers inputs, breadth of checks, JS-off behavior, and operational limits, and an output schema exists so return structure needn't be restated. Nothing essential for correct invocation is missing.

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% and the single url parameter is already documented with a format example, so the description adds no further parameter meaning. Per the calibration rule, baseline 3 is correct when the schema carries the parameter burden.

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?

States a specific verb (load/render) and resource (a page in a real browser at three named viewports) and enumerates exactly what it inspects. It clearly distinguishes itself from siblings by naming get_layout_probe and analyze_layout as the fallbacks.

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?

Explicitly states when to use it (checking the first screen at phone/tablet/desktop) and when not to — when the daily browser budget is exhausted or when the agent has its own browser tool — and routes to named alternatives. Every routing condition is spelled out.

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