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

Annotations only declare the read-only/open-world/idempotency profile; the description goes further by disclosing the return payload shape (final URL, byte size, pixel size), the billing rule ('a page that can't be captured, or renders blank, is not charged'), and a real capability limit around bot protection. These are exactly the traits annotations cannot convey.

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 sentences, front-loaded with the input/output contract before options and caveats. Dense but each sentence carries distinct information (payload, options, limitation/billing); the capability list is slightly compressed but not wasteful.

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 and 10 parameters, the description supplies the missing return-value and failure semantics, which is the main gap it needed to fill. It stops short of mentioning auth/API-key requirements or rate limits, which are the only remaining unknowns for an agent invoking it.

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 every one of the 10 parameters is already documented with ranges, defaults and enums. The description's recap of viewport/fullPage/dark mode/delay/selector adds grouping but little syntax or meaning beyond the schema, so the baseline 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 (capture/screenshot) and resource (a page at {url}) plus the exact output artifacts (JPEG/PNG/WebP/PDF as base64 JSON). It also differentiates itself from the sibling 'unblock', so an agent can route between them without opening either schema.

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 the condition under which this tool is the wrong choice ('does not get past bot protection') and names the alternative to use instead ('use unblock for those pages' text'). That is a clear when/when-not/alternative triad, not mere implied usage.

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