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

Goes beyond the annotations by disclosing that stars are private, never visible to the other party, and synced across the account's devices, plus that the operation is fully authorized, rate-limited and logged. The idempotency claim merely restates idempotentHint=true, but the privacy and auth/rate-limit context is genuine added value. It does not state error behavior for an unknown message_id.

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 short clauses with the operation stated first and the noteworthy privacy behavior immediately after; no padding. The trailing 'idempotent' fragment duplicates an annotation and is the one piece of text that does not earn 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?

For a simple two-parameter toggle with an output schema, the description covers side effects, visibility, cross-device sync, and safety posture — enough to call it correctly. It stops short of describing failure conditions or scope requirements, which for a mutation tool would be the remaining useful addition.

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?

With 0% schema description coverage the description must compensate; it does convey that 'action' selects star versus unstar and that the other input identifies a message, but it adds no format, validation, or scope detail beyond that. The enum and digit pattern live only in the schema, so the description is adequate rather than rich.

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 pair of verbs (star/unstar) and the resource (a message on this WhatsApp account). It is trivially distinguishable from siblings like manage_pin or manage_reaction because the operation itself is named precisely.

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 context is implied through the semantics of a private bookmark, but there is no explicit when-to-use versus when-not-to-use guidance and no routing to alternatives such as manage_pin for related message-state operations.

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