List messages

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 behavioral context beyond those flags: results are ordered most-recent-first, output is limited to compact summary fields, and folder/unread filtering is supported. This is richer than a mere safety flag and gives the agent an accurate mental model of the call.

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 sentences, zero filler. The core action and ordering are front-loaded, scoping is summarized, the return format is specified in parentheticals, and the pointer to get_message is the final sentence. Every sentence earns its place.

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 no output schema, the description properly enumerates the returned fields, so the agent knows what to expect and can distinguish this list tool from get_message. Annotations cover the safety/idempotence profile, and sibling names put the tool in context. Nothing essential for a correct call is missing.

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 description coverage is 100%: all three parameters (top, folder, unread_only) already have descriptive docs. The description echoes folder and unread_only but does not add syntax, defaults, or the meaning of top beyond what the schema provides. This is the expected baseline when the schema does the heavy lifting.

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 opens with the verb-resource pair 'List messages' and immediately specifies ordering ('most recent first'), optional scoping ('folder'/'unread'), and the output shape ('compact summaries with id, subject, from, received, isRead, hasAttachments, preview'). It distinguishes the tool from get_message by pointing out it returns summaries not full bodies, and the sibling search_messages is implicitly separate because this tool lists rather than searches.

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 explicitly routes to get_message for full bodies ('Fetch full bodies with get_message'), giving a clear alternative. It also states when optional scoping applies (folder, unread). It does not explicitly compare against search_messages or state when not to use list_messages, but the context is clear enough for an agent to pick between listing and searching.

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