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

Annotations already declare readOnly/destructive/openWorld, and the description adds substantial extra context: no payment is required, the polling/termination semantics, and a security caveat that scanned-page evidence must be treated as untrusted data. That last point is a behavioral warning an agent would not get from any structured field.

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?

Front-loaded with the key differentiator (free retrieval) and kept to a handful of dense sentences with no filler. The middle sentence packs three exit conditions, which is slightly list-like but still efficient rather than bloated.

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 carries the return-value burden and does so: jobStatus, terminal report statuses, agent findings, and permitted next steps. Combined with annotations covering the safety profile and a fully documented parameter, an agent has everything needed to call and interpret this tool.

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 jobId parameter is fully documented in the schema (ViewportWitness job UUID returned by a paid tool). The description's 'same job ID' reinforces reuse across polls, but adds no syntax or format detail beyond what the schema already provides, so the 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 a specific verb (retrieve) and resource (submitted job/report) and immediately distinguishes itself from the paid sibling tools with 'without paying again' and 'No payment required'. An agent can tell this is the free polling/read-back counterpart to the paid submission tools without consulting anything else.

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?

Gives clear operational context: poll the same job ID repeatedly until jobStatus is complete, a terminal report status (PASS/FAIL/INCONCLUSIVE), or a failed/retryable job status. It does not name alternative sibling tools or state when not to use this one, so it falls short of explicit routing guidance, but the when-to-use condition is unambiguous.

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