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

No annotations are provided, so the description carries the full disclosure burden. It does reveal the capture source, the base64 PNG output, and the addressing mechanism, but it does not mention prerequisites like an active session, side effects, or error behavior. For a simple read-only screenshot operation, the core behavior is nonetheless disclosed.

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?

The definition is compact and purposeful: the first clause defines the action and result, and the second clause handles sibling differentiation. There is no filler, and every sentence earns its place.

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?

Given a single required parameter and no output schema, the description covers what is captured, in what format, and how the target is identified. An agent has enough information to select and invoke this tool correctly without additional context.

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?

The schema only describes sessionId as 'Session ID', so the description adds meaningful semantics by explaining that sessionId is the addressing key that distinguishes this tool from pageId- and udid-based siblings. This is useful context beyond the schema and helps an agent populate the parameter correctly.

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 names a specific verb ('Capture'), resource ('WebDriver session currently showing'), and output format ('base64 PNG'). It also explicitly distinguishes the tool from nearby screenshot siblings by identifier type, so an agent can tell exactly what this tool does.

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 description gives a concrete selection rule: use this when the target is addressed by sessionId. It explicitly contrasts this with web_screenshot (pageId), webpage_screenshot (udid), and device_screenshot/ios_screenshot (udid), making the when-to-use and when-not-to-use decision clear.

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