SDK Domain

The foundation of ts-stack. Contains core cryptographic primitives, Bitcoin Script execution, transaction building and signing, network broadcasting, and lightweight SPV verification. This is the base layer that all other ts-stack packages build on top of.

The core SDK is intentionally standalone with zero runtime dependencies — it works in both Node.js and modern browsers. The optional VeriFast package adds a validated WebAssembly verification backend without changing the SDK's default interpreter.

Packages in this Domain

Common Use Cases

I'm building an application that needs to handle Bitcoin transactions

Start with @bsv/sdk for transaction building, signing, and broadcasting. If you need persistent state and balance tracking, layer @bsv/wallet-toolbox on top.

I'm building a wallet application

Use @bsv/sdk for cryptographic operations and @bsv/wallet-toolbox for the full BRC-100 wallet implementation with storage and signing.

I'm working with tokens

Use @bsv/sdk for low-level script control, or @bsv/btms for higher-level token abstraction.

I need to verify a transaction (SPV)

@bsv/sdk provides full SPV support with MerklePath for merkle proof verification without downloading full blocks.

I need to encode data on-chain

@bsv/sdk's PushDrop class encodes multi-field data in locking scripts, used by overlay protocols like BTMS.

Key Concepts

• Private Key — 256-bit secret that controls UTXOs and signs transactions. Must never be exposed.
• Public Key — Elliptic curve point derived from private key. Used for address generation and signature verification.
• Script — Bitcoin Script bytecode that defines spending conditions. Locking scripts (on outputs) constrain who can spend; unlocking scripts (in inputs) prove authorization.
• Transaction — Atomic unit of blockchain state change. Contains inputs (references to previous outputs) and outputs (new UTXOs).
• UTXO — Unspent Transaction Output. Identified by (txid, outputIndex). Spending requires a valid unlocking script.
• Signature — ECDSA signature with sighash byte indicating which transaction fields are committed to. Used to prove authorization.
• Merkle Proof — Cryptographic proof that a transaction is included in a specific block. Enables SPV without full chain download.
• BEEF — BRC-62 envelope format. Bundles transaction(s) with merkle proofs for offline verification and atomic transmission.
• Wallet Interface (BRC-100) — Standardized interface that all wallets implement. Apps can work with any wallet without code changes.
• Overlay — Layer-2 protocol using on-chain anchors (PushDrop) to build services without modifying Bitcoin consensus.

Quick Example

import { PrivateKey, P2PKH, Transaction } from '@bsv/sdk'

// Create a private key
const key = PrivateKey.fromRandom()
const recipientAddress = '1EvmsbpAY7nESLkN4ajLTMbvsaQ1HpJPGX'

// Build and sign a transaction
const tx = new Transaction(
  1,
  [
    {
      sourceTransaction: Transaction.fromHex('...'),
      sourceOutputIndex: 0,
      unlockingScriptTemplate: new P2PKH().unlock(key)
    }
  ],
  [
    {
      lockingScript: new P2PKH().lock(recipientAddress),
      satoshis: 5000
    },
    {
      lockingScript: new P2PKH().lock(key.toAddress()),
      change: true
    }
  ]
)

// Sign and broadcast
await tx.fee()
await tx.sign()
const response = await tx.broadcast()
console.log('Broadcasted:', response.txid)

What Each Package Provides

@bsv/sdk

• Elliptic curve cryptography (secp256k1), ECDSA signatures, key derivation (BRC-42/43)
• 20+ script templates and Bitcoin Script interpreter
• Transaction builder with fee estimation and broadcasting
• Network integration (ARC, WhatsOnChain, Teranode)
• SPV merkle proof verification
• BRC-100 wallet interface types and WalletClient factory
• Message signing (BRC-18), TOTP, BEEF encoding/decoding
• Storage and KV store abstractions
• Overlay protocol integration (topics, remittance, identity, registry)

When to Use SDK vs. Higher Layers

• Use SDK directly if: You're building a stateless app, you only need transaction building, you want fine-grained Script control, you're implementing a custom wallet
• Use Wallet Toolbox if: You need persistent storage, background monitoring, full BRC-100 wallet, Shamir key sharing, permission management
• Use BTMS if: You're working with tokens, you want token-specific abstractions like issuance/transfer/burn
• Use Wallet Relay if: You need mobile-to-desktop wallet pairing without local key storage

Next Steps

• @bsv/sdk — Full API reference and code examples
• @bsv/verifast — Optional WASM verification backend
• Wallet Domain — Higher-layer packages for persistence and key management
• Guides — Hands-on application and package-boundary examples