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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description still adds value beyond them: the 'cheap' cost signal, the cross-platform return semantics, and the sessionId-addressed scope. It stops short of stating latency or failure behavior when no session/navigation exists.

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?

Front-loaded with the core return contract, then the usage rationale, then the sibling routing. Every sentence carries information, though the parenthetical enumeration of platform behavior is slightly dense for a one-line lookup tool.

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, so the description takes on the burden of describing the return value — and does so precisely (document title vs foreground activity name). Given a 1-param, no-output-schema tool, an agent has everything needed to call and interpret it 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?

Only one parameter (sessionId) and schema coverage is 100%, so the schema already documents it fully. The phrase 'Addressed by sessionId' merely restates the schema and offers no format, sourcing, or validity guidance. Baseline 3 for a fully covered single param.

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+resource ('Return the title of what a WebDriver session is currently showing') and immediately differentiates return semantics per platform (document title for browser, foreground activity name for mobile). An agent can distinguish this from session_page_source or screenshot without opening any schema.

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 names the use case ('confirm a navigation landed where you expected before reading the whole page with session_page_source') and routes to the correct alternatives on a real device (device_current_app or ios_active_app, keyed by udid). Both when-to-use and when-to-use-something-else are given.

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