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

Annotations already declare readOnlyHint/non-destructive, so safety is covered. The description adds genuinely useful context beyond that — the token cost and the cheaper alternative — but says nothing about output size/token magnitude, default viewport behavior, or latency.

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?

Two sentences, front-loaded with the capability and followed by the cost caveat. Zero filler; every clause carries information.

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 7-parameter tool with no output schema, the description covers the mode selection and the main decision driver (cost vs. snapshot). Minor gaps remain around default output type/size and what pdf mode returns, but nothing critical 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 coverage is 86%, so the schema already explains each parameter. The description adds only a loose mapping of the capture modes; it omits pdf, full_res, and the default viewport behavior, so it adds little beyond the structured fields.

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+resource (JPEG screenshot) and enumerates the capture modes (viewport, ref, region, full page), which lets an agent distinguish it from snapshot. It stops short of mapping modes to the pdf/ref/region parameters, but the core purpose is unambiguous.

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 routes the agent to the cheaper alternative: 'snapshot is cheaper', which gives a clear when-to-prefer condition. It doesn't say when a screenshot is actually required over snapshot (e.g. visual rendering or PDF output), leaving that inference to the agent.

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