Verify whether a phone number with country code is registered on WhatsApp before sending messages, adding contacts, or validating recipient details.
Check whether a phone number (digits only, with country code) has WhatsApp.
| Name | Required | Description | Default |
|---|---|---|---|
| phone | Yes | ||
| session | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It implies a read-only check and specifies the phone format, but omits whether the operation requires a valid session, has side effects, is rate-limited, or what happens on error. The word 'Check' suggests safety but does not confirm it.
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?
A single, front-loaded sentence with no wasted words. The format constraint is placed immediately after the resource, which is efficient and clear.
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 and has an output schema, so return values need not be described. However, the required 'session' parameter is completely unexplained, and with no annotations the description should do more to clarify behavior such as session requirements or safety.
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 must compensate. It meaningfully defines the 'phone' parameter (digits only, with country code) but says nothing about the required 'session' parameter, leaving half the inputs undocumented.
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 states a specific verb ('Check') and resource ('phone number has WhatsApp'), making the tool's purpose immediately clear. It does not explicitly differentiate from siblings, but the siblings are session/chat/messaging operations, so overlap is minimal.
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 is implied by the nature of a lookup, but there is no explicit guidance on when to use this tool versus alternatives or prerequisites (e.g., needing an active session). The parenthetical format hint is helpful but does not constitute usage guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.