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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds the return modality — the screenshot comes back as an inline image, not a file path or URL — which is meaningful behavioral context an agent needs to handle the response. 'Read-only' simply restates the annotation and earns no credit.

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 short sentences, front-loaded with the action, then the return format, then the safety trait. No padding, no redundancy beyond the harmless 'Read-only' restatement.

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?

The tool is simple (one required param), safety is fully covered by annotations, and an output schema exists so return values need not be explained in prose. The description covers purpose, precondition and return modality adequately; only the absence of routing guidance to related siblings keeps it from being fully complete.

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% with a single required sessionId, so the schema carries the parameter documentation. The description contributes only the indirect signal that the session must be active; it adds no syntax, format, or meaning beyond what the schema already provides, matching the baseline of 3.

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 the current browser page in an active session'), which is unambiguous and easy to tell apart from siblings like send_task or create_session by name alone. It stops short of explicitly naming or contrasting with any sibling, but the purpose itself is precise.

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?

'in an active session' implies the prerequisite that a session must already exist, which is useful context. However, there is no explicit when-to-use guidance, no statement of when not to use it, and no pointer to which sibling to use instead for related operations.

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