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

Annotations already cover readOnlyHint=true and destructiveHint=false, so the safe-read profile is known. The description adds real value beyond that: 'synced metadata' reveals a dependency on prior sync state, and the ToS/account-restriction warning for the unofficial Wacli client is a meaningful behavioral risk disclosure not present in any structured field.

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?

Two tight sentences: the first front-loads purpose and usage guidance, the second delivers a critical risk warning. No filler, and the ToS warning earns its place because it materially affects whether an agent should proceed.

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?

Has output schema (return values need no explanation), annotations cover the safety profile, and both parameters are documented. The one notable gap is that 'synced metadata' implies a preceding whatsapp_sync call but never states it as a prerequisite; otherwise, a simple search tool is sufficiently 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 100%: both `query` and `limit` carry descriptions in the schema itself. The description adds marginal context by tying `query` to the goal of resolving a JID/number, but it doesn't substantially extend the schema's parameter documentation, so it earns the baseline 3.

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: 'Searches your WhatsApp contacts (synced metadata) by name or number.' The parenthetical clarifies the data source, and naming downstream consumers (whatsapp_send_message, whatsapp_create_group) distinguishes it from siblings like whatsapp_search_messages without ambiguity.

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?

Gives explicit context for when to use it: 'use it to resolve a person to their JID/number before whatsapp_send_message or whatsapp_create_group.' This is a clear precondition or routing signal. It stops short of a 5 because it names no alternatives or exclusion cases (e.g., when to prefer whatsapp_sync or whatsapp_list_chats instead).

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