phone_instances

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description's real contribution is the no-side-effect boundary ('does not start, reconnect or claim') and the non-fallback rule for missing/invalid instances, which prevents a dangerous silent substitution. It stops short of describing the inventory's shape or what read-only status values look like.

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?

Front-loaded with purpose and negative scope, and most sentences carry operational weight. It is dense and slightly instruction-heavy for a zero-argument listing tool, but nothing is 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 no-parameter, no-output-schema read tool, the description covers what is listed, what it is not, failure remediation, side-effect boundaries, and how its results feed into sibling calls. An agent has everything needed to call it and interpret the result correctly.

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?

The tool takes zero parameters, so the baseline is 4 and the schema needs no elaboration. The description's discussion of 'instance' concerns sibling phone_* calls rather than this tool's own inputs, which is useful context but not parameter documentation for this call.

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 ('List installed local iPhone instances') plus the key attribute returned ('read-only status'), then immediately distinguishes this inventory from paired/connected devices so it can't be confused with device-discovery siblings like phone_status or phone_reconnect.

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?

Explicitly sets boundaries ('Does not start, reconnect or claim a phone'), gives a remediation path for recovery_owner=unconfigured (xcrun devicectl list devices, iphone-use doctor on the daemon host), and tells the agent to ask which phone when ambiguous. It also explains the downstream convention of passing instance to any phone_* call.

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