list_folders

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds meaningful reinforcement by explicitly stating 'without changing mailbox state,' which is valuable context confirming the non-mutating guarantee. This exceeds what annotations alone convey by reassuring users about side-effect-free behavior in prose form.

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 a single, efficient sentence with zero wasted words. Everything stated is necessary: the operation (list), the resource (folders), and the non-mutation guarantee. There is no redundant or filler content.

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?

Given the tool has 0 parameters, comprehensive annotations (readOnly, idempotent, openWorld, non-destructive), and an output schema, the description is complete for its simplicity level. It clearly covers purpose and side-effect safety. The only minor gap is lack of explicit guidance about when folder enumeration is needed (e.g., before sending/moving mail), but the output schema and annotations fill most context needs.

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 0 parameters with 100% schema coverage, so parameter semantics concerns are moot. The baseline for 0-parameter tools is 4, and the description doesn't need to add parameter meaning since there are none. The description's state-preservation note is the only semantically relevant addition and it's on point.

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 'List available mailbox folders without changing mailbox state' clearly identifies the verb (list), resource (mailbox folders), and the non-mutating scope. It doesn't explicitly distinguish from siblings, though among sibling tools (search, read, send, trash, move mail), 'list folders' is a fairly unique distinct operation, so differentiation is implicitly clear.

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 context (listing available folders is a read/preparation operation) but does not explicitly state when to use it versus alternatives or mention any exclusions. Since sibling tools are focused on mail items rather than folder enumeration, there's reasonable implicit guidance, but no explicit when/when-not guidance is given.

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