API Reference

Export	Type	Description
HCS21Client	class	Node.js client that inscribes metadata, creates registry topics, publishes declarations, and streams messages via mirror nodes.
HCS21BrowserClient	class	Browser/WalletConnect client for submitting declarations from end-user wallets.
HCS21BaseClient	class	Shared base with buildDeclaration, validateDeclaration, and fetchDeclarations.
PackageDeclaration	type	JSON payload that travels over HCS-21 (p, op, registry, t_id, n, d, a, tags, metadata).
PackageMetadataRecord	type	Optional HCS-1 manifest for extended data (fields such as schema, t_id, description, website, artifacts, etc.).
PackageMetadataPointer	type	Result from inscribeMetadata with pointer, topicId, and sequenceNumber.
PackageDeclarationEnvelope	type	Parsed message returned by fetchDeclarations (includes payer, consensusTimestamp, sequenceNumber).
HCS21_REGISTRY_NAMESPACES	const	Array of supported registry namespaces (npm, pypi, oci, composer, etc.).
buildHcs21CreateRegistryTx	function	Builds a TopicCreateTransaction with the correct HCS-21 memo.
buildHcs21MessageTx	function	Wraps a PackageDeclaration into a TopicMessageSubmitTransaction.

Typings

The module ships TypeScript typings. Example:

import type {
  PackageDeclaration,
  PackageMetadataRecord,
} from '@hashgraphonline/standards-sdk';

These types keep declarations within the 1 KB payload limit and aligned with the HCS-21 specification documented under /docs/standards/hcs-21.