list_devices

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

Since no annotations are provided, the description must carry the full behavioral burden. It does disclose a key API limitation (cannot launch Spotify) and implies a read-only listing operation. However, it omits details like pagination, empty-list behavior, or authentication requirements. While these are not critical for a simple list tool, the description does not explicitly state that it is read-only or describe any error conditions, leaving some behavioral ambiguity.

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 description is composed of two succinct sentences. The first sentence states the core function, and the second adds essential usage context. There is no redundant phrasing, and the most important information (what it lists) appears first. It is appropriately sized and front-loaded.

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 read-only tool with an output schema (as indicated by context signals), the description is complete. It specifies what is returned (devices, including active one), gives usage context, and notes an important API constraint. The output schema can handle return structure details, so no additional explanation is needed. Nothing critical is missing for correct 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?

The tool takes no parameters, so there is nothing for the description to elaborate. The input schema is empty and schema coverage is 100% (trivially). Baseline for a zero-parameter tool is 4, and the description adds no unnecessary parameter information. It is accurate and does not create confusion.

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's function: listing all Spotify devices known to the user's account, including which is active. It uses a specific verb ('list') and resource ('devices'), and the detail about including the active device differentiates it from other list tools like list_user_playlists. The phrasing is unambiguous and immediately conveys the tool's scope.

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 explicitly instructs to use this tool before calling activate_device, and explains why: the Spotify API can only control a device that is already open and cannot launch Spotify from nothing. This provides a clear when-to-use directive and the underlying rationale, which is highly actionable for an agent deciding between tools.

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