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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false, so the agent knows this is a mutating, non-idempotent operation. The description adds the membership/admin prerequisite, which is behavioral context beyond annotations. However, it does not disclose side effects (e.g., notifications to added members), error conditions, or any rate limits. The addition is useful but limited.

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 sentences, front-loaded with the primary action, followed by a key constraint. No fluff or repetition. Every word 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?

Given the tool's moderate complexity, complete schema (100% coverage), output schema present, and annotations covering mutation, the description is adequate. It includes the essential prerequisite for successful invocation. It could optionally mention what happens on failure or whether adding members triggers notifications, but those are not critical for a correct call. The description covers the essential information.

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%, with all three parameters already documented (phone numbers/JIDs format, group JID reference, account reference). The description does not add new semantic meaning about parameters beyond what the schema provides. It does clarify the member format ('by phone number or JID') but that is already in the schema description. 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?

The description clearly states the action: 'Add members to a WhatsApp group by phone number or JID.' This is a specific verb-resource pair that distinguishes it from siblings like wa_remove_participants or wa_promote_participants. The purpose is unambiguous.

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 a clear prerequisite: 'The account must be a member (and, for private groups, an admin).' This tells the agent when the tool can be used. However, it does not explicitly name alternatives or say when NOT to use it, though the distinction from removal/promotion is implicit. The prerequisite is valuable but could go further in routing.

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