list_folders

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

The readOnlyHint annotation already establishes this as a safe, non-mutating read. The description adds real value beyond that by disclosing that the output is a discovery artifact feeding other tools, but it says nothing about mailbox breadth, permissions, or large-mailbox behavior.

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, both load-bearing: the first states the action, the second states when to call it and why the result matters. The primary guidance is front-loaded with no filler.

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?

With an output schema present, the description need not document the returned folder structure, and it correctly focuses on when to call the tool and how to consume its output. It is nearly complete; only the call-ordering relationship with sibling tools could be tightened further.

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 there are no argument semantics to explain; the baseline for a parameterless tool applies. Nothing in the description conflicts with the 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?

"List every folder and label of the mailbox" names a specific verb (list), a specific resource (folders and labels), and its scope (every). This is unmistakably distinct from the email-oriented siblings (list_emails, read_email, search_emails) without needing to name them.

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?

"Use this first when you do not know where a message lives" gives an explicit triggering condition and ordering relative to other tools. It also explains the payoff (returned names are valid inputs elsewhere), which is exactly the routing guidance an agent needs.

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