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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds genuine behavior: ordering by most recent activity and the WhatsApp-specific return fields (external_placement_id, group, within_messaging_window), which tell the agent to expect schema variance per platform.

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, front-loaded with the core action and ordering, then platform scope, then the WhatsApp field caveat. Dense but every clause carries information; the platform enumeration is slightly list-heavy but 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 and only annotation-level safety info, the description does meaningful work by flagging WhatsApp-only return fields and the recency ordering. It stops short of describing the general chat object shape or pagination interaction for non-WhatsApp platforms.

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 100%, so page, after, before, per_page and profile_id are already documented with types and semantics. The description adds no parameter-level detail (e.g., how after/before interact with ordering), so the baseline 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?

Names a specific verb and resource ('List direct-message chats (conversations)') and adds scope ('for a DM-capable profile'), which clearly separates it from dm_messages_list and dm_chat_get. It does not explicitly name those siblings, but the resource noun alone makes the distinction legible.

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?

Usage is implied (enumerate a profile's chats, most recent first) and the supported-platform list gives useful context, but there is no explicit when-to-use rule, no exclusions, and no routing to dm_messages_list for message-level data or dm_chat_get for a single chat.

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