mcp-whatsapp

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

Annotations indicate destructiveHint=true, idempotentHint=false, and openWorldHint=true, but the description adds valuable context: it specifies input format constraints ('digits only (no +)') and implies a batch-checking capability (via array input). This clarifies practical usage beyond the annotations, though it doesn't detail rate limits or auth needs. No contradiction with annotations.

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 extremely concise and front-loaded: the first sentence states the purpose, and the second provides essential input details. Every sentence earns its place with no wasted words, making it easy for an agent to parse quickly.

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 1 parameter with 0% schema coverage, no output schema, and annotations covering safety traits, the description is adequate but incomplete. It explains the parameter well and adds input constraints, but lacks details on output format, error handling, or performance considerations. For a destructive tool (per annotations), more behavioral context would be helpful.

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%, and the description compensates by explaining the 'phones' parameter: it's an array of phone numbers with format 'digits only (no +)'. This adds crucial meaning beyond the bare schema, covering format and constraints. With 1 parameter and no schema descriptions, this is strong compensation.

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 purpose: 'Check which phone numbers are registered on WhatsApp.' This is a specific verb ('Check') and resource ('phone numbers'), though it doesn't explicitly differentiate from siblings like 'search_contacts' or 'get_chat' beyond the WhatsApp registration focus. It's not tautological with the name 'is_on_whatsapp'.

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 no guidance on when to use this tool versus alternatives. It mentions input format ('digits only (no +)') but doesn't specify scenarios, prerequisites, or exclusions compared to sibling tools like 'search_contacts' or 'get_chat'. Usage context is implied but not explicit.

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