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

Annotations declare readOnlyHint=true, openWorldHint=true, and idempotentHint=true, making it a safe, non-destructive read operation. The description adds practical context on how to use the returned IDs and the need to resolve identities, which goes beyond the annotations. It also implies pagination via the 'cursor' parameter, but does not explicitly describe return format or pagination behavior, though this is partially covered by the parameter schema.

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 concise and front-loaded with the primary purpose, followed by a key usage directive. Every sentence earns its place with no fluff or repetition of schema details. It is efficiently structured for quick agent consumption.

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 read-only list tool with no output schema, the description covers the essential context: purpose (identity resolution), key usage guidance (reuse provider user ID), and implied pagination via cursor. With annotations ensuring safety and the schema documenting parameters like account_id, the description is sufficient for an agent to call it correctly. Minor gaps like explicit pagination handling are not critical given the cursor schema.

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 50%, covering the 'cursor' and 'account_id' parameters. The description adds no additional parameter-specific information; it focuses on usage of the output. Since half the parameters are undocumented in the schema (limit, offset) and the description does not compensate, a baseline 3 is appropriate. The description's mention of resolving identities does not clarify parameter semantics further.

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 'List WhatsApp contacts' and elaborates its purpose: to resolve a human name/phone to an exact provider user identity before starting a chat. This distinguishes it from similar sibling tools like 'messaging_resolve_recipient' and 'whatsapp_list_conversations' by focusing on enumerating contacts for identity resolution.

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 explicitly advises to reuse the returned provider user ID and warns not to pass display name as whatsapp_user_id, which provides clear guidance for using the output. It implies use before starting a new chat, but does not explicitly contrast with alternatives like 'messaging_resolve_recipient' or 'whatsapp_is_number_registered', which could have strengthened the guidance.

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