folder_stats

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

With no annotations, the description carries full burden. It discloses the live nature, the fact that no messages are fetched, and the speed/accuracy tradeoff of scanLimit. It does not explicitly mention read-only or side-effect-free behavior, but 'without fetching messages' strongly implies it. This adds meaningful context beyond the schema.

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?

Three dense sentences: core function, use case, and explicit alternatives. Every sentence earns its place, with no redundancy or 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?

Given the simple two-parameter input and lack of output schema, the description provides return value names, use cases, alternatives, and performance tradeoffs. It is complete for a lightweight read-only stats tool.

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 schema already covers both parameters completely, including defaults and the speed/accuracy tradeoff. The description adds no new parameter-level detail, so the baseline of 3 applies.

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 returns live message count, unseen count, uidNext, and uidValidity for a single mailbox folder. It distinguishes itself from sibling tools by specifying it does so without fetching messages.

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?

It explicitly states when to use the tool (checking unread counts or folder health) and provides alternatives: count_messages for filtered queries and get_email_stats for aggregate summaries. This is strong when/when-not guidance.

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