List devices

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

Annotations already declare readOnlyHint=true, so the description's statement 'sends no SMS' adds behavioral context beyond annotations, reinforcing the read-only nature. It also mentions the details of what is returned (last checked-in time, message counts), which is transparent. No contradiction; the description complements the annotations well. The 4 reflects solid but not exhaustive behavioral detail (e.g., no mention of data freshness).

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 fluff, with the purpose and key content in the first sentence and usage triggers in the second. The description is efficiently structured and front-loaded, every sentence adds value.

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 list operation with no parameters and no output schema, the description fully covers what it does, what it returns (list of fields), when to use it, and what it doesn't do (no SMS). An agent has all necessary information to call it 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 has zero parameters, so the baseline is 4. The description explicitly states 'Takes no arguments,' aligning with the empty schema and leaving no ambiguity about parameter expectations. Nothing more is needed.

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 clearly states the tool lists Android phones registered to the account, enumerating the specific fields returned (id, name, enabled state, default sender, last check-in, message counts). It uses a specific verb 'list' and a clear resource, distinguishing it from send_sms by explicitly noting it sends no SMS.

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 explicit when-to-use triggers: 'when a send fails with a device error, when the user asks which phone will be used, or when you need a device_id.' It also implies exclusion from sending by stating 'sends no SMS,' giving clear guidance on when not to use it (for sending). This is complete and actionable.

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