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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds a real precondition beyond annotations: the phone must show 'video_live: true' in list-phones-tool, which prevents failed calls. It doesn't discuss output size or error behavior, keeping it just short of 5.

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 with the core action front-loaded, followed by use context and then the precondition. No filler; every sentence carries distinct information.

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?

With no output schema, the description correctly states the output type (JPEG snapshot) and the key precondition. It is complete for a simple two-parameter read tool, though it could note the resolution default or failure mode more explicitly.

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%, so both the slot UUID format and the width range/default are already fully documented. The description's 'video_live: true' note reinforces the slot precondition but adds no new parameter mechanics, so the 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?

States a specific verb and resource ('Capture a JPEG snapshot of a farm phone screen') and distinguishes itself from phone-ocr-tool and phone-control-tool by defining its role as visual state inspection. An agent can immediately tell what this produces without opening the 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?

'Use it to see what is on screen before and after phone-control-tool input' gives a clear usage context and ties it to a specific sibling. It stops short of explicit when-not guidance or naming alternate inspection tools like phone-ocr-tool, but the intended workflow is unambiguous.

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