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

With no annotations, the description carries the full burden and does disclose a notable behavioral trait: the 90-second timeout and extension via caller-supplied budget. It also clarifies that system mode triggers platform-native back behavior. It could mention side effects like exiting the app, but the provided details are meaningful.

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 tight sentences, each earning its place: the action, the mode-selection guidance, and the timeout behavior. The most important information is front-loaded and there is no filler.

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 navigation command with a rich schema and an output schema, the description covers the core decision (mode choice) and a key behavioral constraint (timeout). It does not discuss device-resolution details or potential exit behavior, but those are less critical for correct invocation given the schema's high coverage.

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 description coverage is 95%, so the baseline is 3, but the description adds real semantic value by explaining the mode parameter's two values: in-app for the app navigation stack and system for platform back behavior. This goes beyond the raw enum and helps the agent pick 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 states a specific action—'Navigate back in the app or through system navigation'—and clearly distinguishes the two modes it supports. This separates it from sibling navigation tools like home and app-switcher without ambiguity.

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 explicit guidance on when to use each mode: in-app for the app navigation stack and system for platform back behavior. It does not name alternative tools like gesture or swipe, but the mode-level guidance is clear and actionable.

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