HCS-21 Standard

The Brain
of the Operation

We built HCS-16 Appnets to connect the world.Now, HCS-21 Adapters give them something to think about.

An Empty Shell
is Useless.

HCS-16 Floras are powerful coordination engines. They provide the body: the secure multi-sig accounts, the communication channels, and the state storage.

But a body without a brain can't act. Without shared logic, nodes have nothing to agree on. They need a way to process information deterministically.

"We have a quorum, but what are we voting on?"

HCS-16 Idle State
🧠
NODE 1
NODE 2
NODE 3
NODE 4
HCS-21 Active Consensus

Injecting
Logic into the Network.

HCS-21 Adapters are the deterministic "cartridges" you plug into an Appnet.

They contain the source code, schema, and consensus logic needed to process data. Whether it's fetching an oracle price, verifying a credential, or running an LLM agent—the Adapter ensures every node runs the exact same calculation.

  • Deterministic: Same input = Same output, everywhere.
  • Verifiable: Inscribed on-chain manifests.
  • Portable: Use standard registries like npm or PyPI.

How It Comes Together

From configuration to consensus, see how HCS-16 and HCS-21 interact.

File: flora.yaml
flora:
account: 0.0.9876
adapters:
- adapter_id: "npm/@hol-org/price-oracle@^1.2"
required: true
config:
pair: "HBAR/USD"
Live Implementation

Real-World Example: Flora Price Oracle

Three independent adapters. One verifiable price.

Source A
Binance
$0.05235
Latency: 12msHash: 7c4f1a...
Source B
CoinGecko
$0.05235
Latency: 45msHash: 7c4f1a...
Source C
Mirror Node
$0.05235
Latency: 8msHash: 7c4f1a...

Ready to wire up the brain?

Join the decentralized intelligence network. Build adapters that make the entire ecosystem smarter, faster, and verifiable.