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

The description adds value beyond annotations by specifying the return format ('as an inline image'), which the schema does not explain. The 'Read-only' statement aligns with the readOnlyHint, and no contradictions exist.

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?

Two sentences, front-loaded with the core action, and zero filler. Every word earns its place, and even the redundant 'Read-only' is short and reinforces the annotation.

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 description is complete for a simple tool: it states the action, the context requirement, and the return format. With an output schema present, the tool doesn't need to spell out the full response structure. Minor details like full-page vs. viewport capture are not essential.

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%, so baseline is 3. The description adds contextual meaning to sessionId by specifying it must be an active session, which goes beyond the simple 'Session ID' schema description.

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 states a specific action ('Capture a screenshot'), a specific resource ('current browser page'), and a condition ('in an active session'). This clearly distinguishes it from sibling tools like list_sessions or browser_task, which have different purposes.

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 phrase 'in an active session' clearly indicates that a pre-existing, active session is required, implying a prerequisite of creating a session first. There are no competing screenshot tools, so no exclusions are needed, but it doesn't explicitly outline when not to use it.

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