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

With no annotations, the description carries the behavioral disclosure burden. It clearly states the key async contract: 'the call only acks the start; the agent streams progress separately.' This is meaningful beyond the name and schema. It does not cover failure modes, cancellation, or permissions, but the core invocation behavior is transparent.

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 definition is two sentences with no filler: the first states purpose, the second states the async execution contract. Both parts of the second sentence add necessary behavioral information. It is front-loaded and easy to scan.

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?

The async contract is described, which matters because there is no output schema. However, the description does not point to get-phone-run-tool or list-phone-runs-tool for observing the streamed progress, nor does it clarify what 'narrow task' excludes. For a 2-parameter async tool this is adequate but leaves meaningful gaps.

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 schema already gives detailed meaning for both parameters: slot must be a UUID from list-phones and must be cast/live, while task is a plain-language instruction. The description adds only the 'narrow task' qualifier, which is modest extra semantics. Baseline 3 is appropriate because the schema carries the parameter documentation load.

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 first sentence names a specific action ('ask ... to carry out') and resource ('on-phone GUI agent,' 'farm phone'), making the tool's purpose clear. It does not explicitly contrast with siblings like run-macro-tool or phone-command-tool, but 'GUI agent' and 'narrow task' provide enough differentiation. 'Narrow' is somewhat vague but not misleading.

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?

There is no explicit when-to-use or when-not-to-use guidance, and no sibling alternatives are named or excluded. The phrase 'narrow task' implies a scope limit, but the description does not say to prefer get-phone-run-tool for checking results or phone-command/run-macro for scripted operations. An agent selecting among the many phone-related siblings must infer placement.

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