detect_message_service

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

With no annotations, the description carries the disclosure burden and does well by explicitly stating 'This is best-effort because Apple does not expose a direct preflight availability API.' This warns the agent about reliability limitations. It does not elaborate on possible failure modes or whether the tool is read-only, but 'inspect' implies no mutation.

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?

Two sentences, no filler, front-loaded purpose statement, and a meaningful caveat. Every sentence earns its place.

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 two-parameter pre-send detection tool, the description covers the core behavior, output categories (iMessage, SMS/RCS, or auto), and the key limitation. It lacks a detailed return structure, but the described output types are sufficient for agent invocation.

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 the schema already documents both parameters. The description adds no parameter-specific detail beyond implying the recipient in 'for a recipient,' so the baseline of 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 uses a specific verb-resource pairing: 'Inspect local Messages history for a recipient and recommend iMessage, SMS/RCS, or auto before sending.' It clearly distinguishes itself from sending tools like send_message and read/search tools by focusing on pre-send service detection.

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 provides clear context: use this before sending to determine the best message service. It does not explicitly name alternative tools or state when not to use it, but the 'before sending' phrasing gives a practical usage trigger.

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