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

Annotations already declare readOnlyHint and idempotentHint, so the description correctly avoids restating those. It adds behavioral value by explaining that the returned folder.id is essential for downstream operations and by cautioning against using human names. These details go beyond the structured annotations and help the agent understand the tool's role in a workflow.

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 only three sentences, but it contains redundancy: the need for folder.id is mentioned twice ('Returned folder.id is required' and 'Obtain with: email_list_folders -> folder.id'). This repetition could be trimmed without losing meaning. The main purpose is front-loaded, but the wording is not maximally concise.

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 simple listing tool with no output schema, the description covers the essential context: it explains what the tool returns (folder.id), when to use it (first step for IMAP), and a critical pitfall (never pass human names). It does not discuss pagination or account selection, but those are documented in the schema. Given the tool's simplicity, this is adequately complete.

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?

Schema coverage is 67% – cursor and account_id have descriptions, while limit only has min/max bounds. The description does not elaborate on any parameter semantics, but the schema already covers the important ones. Since coverage is moderate and the description adds nothing about parameters, a baseline score of 3 is appropriate.

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 action ('List') and the resource ('Gmail labels, Outlook folders or IMAP folders'), making it obvious what the tool does. It also distinguishes itself from siblings by emphasizing that the returned folder.id is required by folder-specific operations, setting it apart from email_list_folder_messages or email_get_folder.

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 provides useful usage context: it notes that for IMAP this is normally the first step before listing messages, and warns against passing human-readable folder names when an ID is required. However, it does not explicitly name alternatives like email_resolve_folder or email_get_folder, so the guidance is implicit rather than fully explicit.

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