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

Annotations already declare readOnly/openWorld/non-destructive, but the description adds value they don't carry: the return is an image only, and the ~45 s timeout yields 'still opening; call screenshot again' or 'still working; call screenshot again'. That retry semantics is genuinely useful operational context; only the exact image format/size is left unstated.

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 purpose, then usage restraint, then timing behavior. Dense and mostly waste-free, though the opening sentence is a run-on that could be split for clarity.

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?

No output schema exists, and the description does cover the return type plus the retry messages, which is exactly the missing piece. The remaining gap is identifier provenance for the two required params, which is left implicit.

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 0% and both parameters (page, candidate) are required with no documentation. The description only obliquely implies that 'page' is an open page and 'candidate' is an entry in the Candidate tree, without saying how to obtain either identifier (e.g., from open_page or read_panel output). With 0% schema coverage the description should compensate and it largely does not.

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 output (an image of one candidate of an open page, 'and nothing else') and implicitly contrasts with workspace_image and the Candidate tree. The intended use case (content text can't describe — canvas chart, image) sharpens the purpose further, though the phrasing is slightly convoluted.

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 says to use it sparingly because 'the Candidate tree usually says enough', which gives a clear when-not condition and points at the textual alternative. It doesn't name the specific sibling tool to prefer, so the agent must infer that read_panel is the substitute.

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