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

With no annotations, the description carries the burden of behavioral disclosure. It explains the action's nature ('browser's Back' or 'platform back action') and the absence of a forward counterpart. While it doesn't detail error handling or edge cases (e.g., empty history), for a simple navigation operation this is adequate. It lacks explicit side effects but does not contradict any known behavior.

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 description is concise, three sentences, with the core purpose front-loaded in the first sentence. It efficiently includes context about mobile vs. browser and alternatives without unnecessary words. Every sentence contributes to understanding.

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?

For a tool with a single parameter and no output schema, the description is complete. It explains the action, the parameter's role, and provides routing to alternatives. No additional information is needed for an agent to call this tool correctly.

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% since sessionId has a description ('Session ID'), and the tool description only mentions 'Addressed by sessionId' without adding further detail beyond the schema. The baseline is 3 for full coverage; the description does not enhance parameter meaning beyond confirming the parameter's role.

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 clearly states the specific action ('Go back one entry in the history of a WebDriver session'), distinguishes between browser and mobile contexts, and explicitly names alternatives (web_back, web_forward, webpage_back, device_key) for other surfaces. This makes it unambiguous and easily differentiated from siblings.

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 provides explicit when-to-use guidance: it specifies that this tool is for 'WebDriver session' and that there is no forward counterpart. It then directs the user to use web_back/web_forward for desktop grid pages and webpage_back/device_key for real devices, effectively covering alternative scenarios.

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