Take a screenshot

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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the safety profile is covered. The description adds genuinely non-derivable context: cookie banners are auto-hidden, the cost is '2 credits', and desktop/mobile/full-page modes are supported. That is real value beyond the structured fields.

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 tight sentences, front-loaded with the core action and result, followed by capability and cost details. Every sentence earns its place with no redundancy or filler.

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?

With no output schema, the description usefully clarifies that the tool returns an image, and it discloses cost and cookie handling. For a simple read tool, an agent has enough to invoke it correctly, though it could state whether large full-page captures have size limits.

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 with dimensions and defaults. The description's mention of 'desktop, mobile and full-page captures' maps to device/full_page but adds no syntax or meaning beyond the schema, so the baseline of 3 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 a specific verb and resource ('Capture a screenshot of a web page and return the image') and makes the output type explicit ('so you can see how the page looks'). This cleanly distinguishes it from siblings like url_to_markdown, extract_metadata, and extract_images, which return text or asset URLs rather than a rendered image.

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 phrase 'so you can see how the page looks' implies the use case (visual inspection), but there is no explicit guidance on when to choose this over the sibling extraction tools, nor any when-not conditions. Usage is implied rather than stated.

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