Check WhatsApp Numbers

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is known. The description adds useful context about the return value (existence and JIDs), which helps the agent understand behavior beyond the schema. It does not go into rate limits or side effects, but those are less critical given the read-only nature.

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?

The description is two sentences, front-loaded with the core function and return value. No filler or repetitive content. Every word contributes to understanding the 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?

The tool is simple with one parameter fully documented in the schema. Although there's no output schema, the description clearly states what the tool returns (existence and JIDs). This is sufficient for an agent to select and invoke the tool correctly.

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?

The schema already fully documents the single parameter 'numbers' with format guidance and examples. The description adds no additional information about parameters; it focuses on the return value. Baseline for 100% schema coverage is 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?

The description clearly states the tool's function: 'Verify if phone numbers are registered on WhatsApp' and specifies the output 'Returns which numbers exist and their JIDs.' This distinguishes it from sibling messaging and contact tools.

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 implies its use case (pre-contact verification) but doesn't explicitly state when to avoid it or mention alternatives. Since it's a unique checking tool among siblings, the context is clear, but there's no explicit exclusion or alternative guidance.

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