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

Annotations already establish readOnly, idempotent, and non-destructive behavior, so the description does not need to restate those. It adds valuable context about the headless-browser rendering and, importantly, the return behavior—metadata about the base64 PNG length rather than the full blob. This gives the agent an accurate expectation of what the tool will actually produce.

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 compact and efficient: one sentence states the core action and rendering context, one sentence states the return behavior, and the example shows the exact invocation shape. Every sentence earns its place with no 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 simple two-parameter tool with rich annotations, the description covers the key invocation facts: what it does, how it renders, what it returns, and an example call. The lack of an output schema is mitigated by explaining the return format. Minor gaps like error handling or screenshot size are not critical for selection and 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?

The input schema already describes both parameters fully, and the description's example mirrors the schema's example. Since schema description coverage is 100%, the baseline of 3 applies; the description adds no substantive parameter meaning beyond what the schema provides.

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 opens with a specific verb and resource: 'Capture a screenshot of a web page via Zyte API (rendered in a headless browser).' It also clarifies a key behavioral nuance—returning only metadata about the PNG length rather than the full blob—which makes the tool's exact scope unmistakable. This is sufficient to distinguish it from sibling tools like zyte_fetch or zyte_extract.

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 gives no guidance on when to prefer this tool over alternatives, nor does it mention sibling tools such as zyte_fetch or zyte_extract. The example shows how to call it, but the agent must infer the appropriate use case from the tool name and general phrasing.

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