List allowed roots

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering safety. The description adds valuable context: the tool returns the set of allowed roots and that file tools enforce this restriction. This goes beyond the annotations by explaining the relationship with file tools, which is useful behavioral information.

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 two sentences with zero waste. The first sentence states the primary function, and the second provides the key behavioral context (enforcement). It is perfectly front-loaded and every word 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 no-parameter, read-only tool, the description covers its purpose and the reason it matters. It could explicitly mention the return format (e.g., absolute paths), but the output is simple and the enforcement note adds completeness. No output schema exists, so the description carries the burden, but it is largely sufficient.

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?

There are zero parameters, so the description needs to explain nothing about parameters. The baseline for 0 params is 4, and the description correctly omits any parameter detail since none exist.

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 and resource: 'List directories' that are allowed roots. It clearly states the tool's function and adds context that these are the only directories the server can read/write. It doesn't explicitly differentiate from siblings like list_directory, but the scope is obvious and distinct.

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 implies usage: it tells you that file tools reject paths outside these roots, so the agent can infer this tool is used to know valid paths before invoking file tools. However, it does not explicitly state when to use this versus alternatives, or provide exclusion conditions. The guidance is implicit rather than explicit.

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