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

Goes well beyond the readOnlyHint annotation: it states nothing can be sent, that results are newest-first, that only synced messages are present, that group events are skipped, and includes an explicit prompt-injection warning about treating message text as data. These are exactly the behavioral traits an agent needs before calling.

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?

Dense, front-loaded sentences with no filler; each one adds a distinct fact (scope, ordering, parameter formats, data caveats, safety warning). Sized appropriately for a 4-parameter search tool.

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?

Output schema exists so return values need not be explained, and everything else an agent needs — scope, ordering, filter semantics, format strings, coverage limits, and injection safety — is covered.

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 0%, so the description carries the full burden — and it does: query matching semantics (case-insensitive text match), chat accepted forms (chat id from conversation_id, partial contact/group name, phone number), and since formats (ISO date or unix seconds). Only `limit` is left undocumented, a minor omission.

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?

States a specific verb and resource plus a precise scope: messages from the WhatsApp desktop app on this Mac, newest first. The read-only constraint and the sync limitation distinguish it clearly from siblings like get_whatsapp_chat (single conversation) and search_messages (non-WhatsApp).

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?

Explains the no-filter default ('With no filter it lists the newest messages') and the data availability caveat ('only what the desktop app has synced'), which tells the agent when results may be incomplete. It does not explicitly route to a sibling such as get_whatsapp_chat or search_messages, so the alternative-selection guidance is implied rather than stated.

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