mail_list_mailboxes

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

With no annotations, the description carries the full burden. It discloses that the tool returns all mailboxes, explains the data model (folders/labels, parentId for nesting, role for system mailboxes), and implies a read-only operation. It adds value beyond the empty input 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?

The description is a single paragraph that includes both factual listing and conceptual explanation. It is fairly concise but the background on folder/label semantics could be shortened or moved to documentation. Still, every sentence adds value.

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 an output schema exists (though not shown), the description adequately explains what is returned and provides context on the mailbox hierarchy and system roles. It is complete for a list 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 input schema has no parameters, so schema coverage is 100%. The description adds no parameter information because none exists. Baseline for no parameters is 4.

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 lists all JMAP mailboxes with specific fields (id, name, role, email counts, parentId), and explains the distinction between folders and labels in Fastmail. This is a specific verb-resource combination that distinguishes it from siblings like mail_create_mailbox or mail_delete_mailbox.

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 for retrieving a full list of mailboxes, but does not explicitly state when to use it versus alternatives (e.g., when to use mail_list_mailboxes vs. mail_get_email or mail_search_emails). It lacks explicit when-not-to-use guidance.

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