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

With no annotations provided, the description carries the full burden, and it delivers: it discloses the slow path, base64 PNG return format, auto-wake and single retry behavior, and the active-session requirement with auto-start behavior. These are beyond what the schema could express.

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 compact and front-loaded with the core purpose, then moves to alternatives and behavioral caveats. Each sentence adds necessary information, though a little redundancy exists between 'slow full-fidelity path' and 'full-fidelity frame', which prevents a perfect score.

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 screenshot tool with no output schema, the description covers the return format, speed trade-off, alternative tools, device-sleep behavior, and session prerequisites. The single parameter is fully documented in the schema, so nothing needed to call it correctly is missing.

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 100% and the only parameter, udid, is documented as 'iOS device UDID'. The description does not add meaning about the parameter, but it does not need to because the schema already fully explains it, matching the baseline for high schema coverage.

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 and resource: take a HIGH-FIDELITY screenshot of an iOS device. It also distinguishes itself from the sibling ios_mjpeg_screenshot by calling itself the slow full-fidelity path, so an agent can tell them apart immediately.

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?

It explicitly says to prefer ios_mjpeg_screenshot for routine per-action checks and to reserve ios_screenshot for crisp full-fidelity frames. It also gives conditions for using ios_fast_screenshot when no session is running and one should not be started, making the routing decision unambiguous.

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