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

With no annotations, the description carries the full burden. It discloses the session requirement and that it can auto-start a session—a potential side effect—and states the return value is a URL string. However, it does not explicitly confirm read-only behavior, error handling, or what happens when Safari has no URL or isn't running.

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 two sentences with zero redundancy. The first sentence states the core purpose and return type, and the second adds the prerequisite. Every word earns its place and key information is front-loaded.

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 simple getter with one parameter and no output schema, the description covers the purpose, return type, and session prerequisite. It doesn't cover edge cases like Safari not running or empty URL, but those are minor for a tool of this simplicity and could be deferred to an output schema or error messages.

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%—the single required parameter 'udid' is described as 'iOS device UDID' in the schema. The description adds no additional parameter meaning beyond what the input schema already provides, so baseline 3 applies.

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 verb ('Get') and resource ('current URL loaded in Safari on an iOS device'). It clearly identifies the platform (iOS) and browser (Safari), distinguishing it from generic tools like device_get_browser_url without opening schemas.

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 mentions a prerequisite (active iOS automation session) and auto-start behavior, giving some contextual usage guidance. However, it does not name sibling alternatives like ios_safari_navigate or explicitly state when not to use this tool, leaving when-to-use to inference.

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