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Documentation Index

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USync is WhatsApp’s directory protocol. It is what powers onWhatsApp() checks, LID/PN resolution, device list lookups, and similar metadata queries. Baileys exposes USync directly so you can build extended functionality without reimplementing the wire format.
USync support inside Baileys is intentionally low-level. If a high-level helper exists for what you’re trying to do (onWhatsApp, group metadata, getLIDsForPNs, etc.), prefer that — USync is meant for cases where no helper covers your use case.

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When to use USync

Reach for USync when you need to:
  • Resolve phone numbers to LIDs in bulk (getLIDsForPNs is the high-level wrapper).
  • Query device lists for users you communicate with.
  • Probe metadata WhatsApp exposes via the directory but Baileys doesn’t yet wrap.

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Building a USync query

Baileys exposes the USync protocol classes on the socket. A query consists of:
  1. A query type (for example, contact lookup or device list).
  2. A list of users to look up, identified by JID/PN/LID.
  3. The protocols (sub-queries) you want returned for each user — contact info, devices, LID mapping, business metadata, and so on.
Refer to src/WAUSync in the Baileys repository for the canonical list of query and protocol classes. Each protocol exposes a typed result shape so you know exactly what fields come back.

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MEX queries

Baileys also supports MEX (the GraphQL-like query layer WhatsApp uses internally) for surfaces such as channel metadata, communities, and product catalogs. MEX queries are sent through the same socket and are typically wrapped by higher-level helpers — search for executeUSyncQuery and similar internal helpers in the source for examples you can adapt.

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Caveats

  • WhatsApp can rate-limit aggressive USync queries. Batch lookups when possible.
  • Schemas occasionally change as WhatsApp evolves. If a query starts returning unexpected results, check the latest Baileys source for an updated protocol definition.
  • USync is undocumented externally — anything in this area is subject to change without notice from WhatsApp.