list_controllers

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

With no annotations, the description carries the full burden and does disclose real behavior: the fallback resolution order (explicit argument → select_controller → default) and the per-session selection state. It does not explicitly label the operation read-only, but 'List' and the framing make the non-mutating nature unambiguous.

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 the purpose in one line, followed by genuinely useful resolution context. The 'Returns' block partially restates what the output schema already provides, which is the only mild redundancy.

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 zero-parameter discovery tool with an output schema, the description supplies enough context: what it lists, how results are used, and how the default is resolved. The return enumeration duplicates the existing output schema rather than adding to it.

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. The description also usefully clarifies the meaning of the `controller` argument on sibling tools, adding semantics beyond this tool's empty schema.

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 states a specific verb+resource ('List the UniFi controllers this server can reach') and defines the scope of the read. It is clearly separable from siblings like select_controller, get_active_controller, and the many list_integration_* tools, which target other resources.

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 explains the downstream usage pattern (every controller-bound tool takes a `controller` argument drawn from this list) and names the resolution chain via select_controller and the default. It effectively tells the agent why and when to call this, though it does not explicitly state exclusions or a 'call this before X' prescription.

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