Screenshot

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

Beyond the readOnly/openWorld annotations, it discloses a genuinely non-obvious artifact: a glass arrow overlay indicating the last action's target, with instructions for interpreting it as a mis-click signal. It also states the output format is JPEG. It stops short of describing image size, cost, or viewport-vs-fullpage behavior, which keeps it at 4.

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?

Three short sentences with the core capability first, then the interpretation caveat, then the routing advice — all front-loaded and waste-free. The middle sentence is dense and slightly meandering with its parenthetical and double clause, costing it the top mark.

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 one-optional-parameter read tool with annotations and no output schema, the definition covers purpose, alternatives, output format, and the misleading-arrow pitfall. It leaves 'current tab's screen' implicit about viewport vs full-page capture, but nothing essential to 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 coverage is 100% and the single `ref` parameter is already documented as 'one element to capture; the whole screen if omitted'. The description restates the same omitted/not-omitted behavior without adding format, syntax, or lookup guidance for refs, so the 3 baseline applies.

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 exactly what is returned (a JPEG of the current tab's screen, or one element by ref), which uniquely identifies this as the visual capture tool. It also names the two siblings it competes with (browser_snapshot, browser_get_text), so an agent can separate it from the reading tools without inspecting schemas.

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?

'Only when layout, images or a canvas matter' is an explicit usage gate, and the same sentence names the cheaper alternatives that should be preferred otherwise. That is a when-to-use plus a when-not-to-use plus named alternatives in one clause.

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