A self-contained, single-file Bitcoin wallet that runs entirely in the browser — think bitaddress.org, but a modern BIP84 HD wallet from a seed phrase that scans history, watches for payments, spends on-chain, pays Lightning invoices, and holds an off-chain balance on Ark. The whole wallet is one static index.html you can save and run offline, forever.

Live at https://halwallet.app (the built index.html also runs straight from the filesystem with no server).

The name is a nod to Hal Finney.

• BIP84 / native SegWit (p2wpkh) HD wallet from a 12-word BIP39 seed (imports any valid BIP39 phrase; optional passphrase).
• Per-wallet networks — each wallet is stamped with its network (mainnet, testnet, signet, mutinynet, regtest); switching wallets switches networks, and wallets on different networks coexist in one session.
• One fresh address at a time — a new receive address is only handed out after the current one is paid, so used addresses stay contiguous and scans stay tiny (no 20-address gap probing).
• Choose your data source — Electrum-over-WebSocket servers or Esplora REST explorers, per network, with silent failover — or point it at your own node.
• Real-time incoming-payment push over WebSocket where the source supports it, with polling + periodic reconcile as the fallback. Replaced (RBF) transactions are detected and pruned from history automatically.
• Spending with proper coin selection + fee estimation (@scure/btc-signer), multiple recipients, a fee-rate picker, send-max, manual coin control, and a QR scanner (address / BIP21 / signed tx).
• Offline / air-gapped signing — export a keyless snapshot on an online device, sign on an offline one, broadcast anywhere.
• Installable PWA, global sats/BTC toggle, 19 languages.

A native-JS Ark client (speaks gRPC-web + MuSig2 directly to bark/captaind servers — no WASM, no new dependencies, ~2k lines):

• Board on-chain coins into an Ark server; send and receive instantly off-chain with zero mining fees; server fees shown before anything moves.
• Refresh / consolidate vtxos (the round-based maintenance that resets expiry and chain depth).
• Collaborative offboard — move the whole Ark balance back to your own on-chain address in one server-cosigned transaction.
• Unilateral exit — the trustless backstop: publish the vtxo's pre-signed transaction chain on-chain (CPFP-bumped, TRUC-aware, one confirmed hop at a time), wait out the CSV timelock, and claim with your key alone. Works even if the server is gone; live progress (hop counter, blocks-left countdown) in Settings.
• Ark gifts — bearer gift links whose secret is the link: claimed instantly and free, even into a brand-new empty wallet with zero on-chain footprint. Revocable until claimed.
• Crash-safe by construction: every multi-step ceremony checkpoints to storage around each server round-trip, and local state reconciles against the server's authoritative vtxo status before money moves.

• Pay bolt11 invoices and receive over Lightning via Boltz-compatible submarine swaps — non-custodial either way: a provider can fail a swap but never take funds (claims/refunds are enforced on-chain). Pick a provider per network or point at your own.

• A static, publicly shareable BIP-352 silent-payment address (sp1…); every payment lands at a fresh unlinkable on-chain address. Scanning uses a configurable (self-hostable) tweak indexer, with the EC math in a Web Worker and a chunked, resumable catch-up scan.

• Gift links — presigned bearer transactions claimable by whoever opens the link, straight into a fresh wallet (with seed backup flow) or an existing one. Reclaim or revoke unclaimed gifts. Optionally lock a gift to a nostr account (the claim code is DM'd to them; the link alone is not enough).

• Optional encrypted state sync over Nostr — wallet state NIP-44-encrypted to yourself as a replaceable event, per network, on relays you choose. The nostr identity derives from the same seed (NIP-06).

Every feature above is a plugin behind a build seam. HAL_FEATURES selects what ships; excluded features never enter the bundle — their code, their network endpoints, their crypto:

bun run build                          # everything (~610 KB)
HAL_FEATURES=ark,gifts bun run build   # core + ark + gifts
bun run build:minimal                  # core on-chain wallet only (~320 KB)

tools/minimal-smoke.js verifies the minimal profile is a fully working on-chain wallet with zero feature code in the bundle. Features integrate through fixed seams on the core (registerCoinLock, registerInputSigner, cache extensions, UI hooks), so a stripped build isn't a crippled build — it's the same core wallet, smaller.

Requires Bun.

bun install
bun run dev      # http://localhost:5173 (rebuilds on each refresh)

The dev server also proxies local regtest backends (electrum, esplora, boltz, SP indexer) so the app works unchanged from a phone on the LAN. End-to-end suites in tools/ drive a headless Chrome through the real flows (boarding, ark sends, offboard, unilateral exit, gifts, swaps, silent payments) against a local regtest stack.

bun run build    # → dist/  (index.html + PWA sidecars)

dist/index.html inlines all code, the crypto/QR/Nostr libraries, and the CSS — save that one file and open it directly in a browser, no server or internet needed. The build also emits PWA extras (manifest.webmanifest, sw.js, icons, and a lazy-loaded jsqr.js) for the hosted site; they're optional and simply 404 when index.html is opened on its own.

Three layers, fastest first:

1. sessionStorage — keeps the wallet open across a refresh (cleared on logout / tab close).
2. localStorage — caches scanned state per wallet and per network, so a reload shows balances instantly.
3. Nostr — encrypted, replaceable cross-device state per network (when sync is enabled).

On load and on a timer the wallet reconciles against its data source; a manual Settings → Rescan forces a full re-scan on demand.

• Self-custody software handling real keys — review the code before trusting it with funds. It's a hot wallet (keys live in the browser); for large amounts use a hardware signer or run it air-gapped.
• The seed/passphrase live in memory while the page is open and in sessionStorage for the tab session; locking or closing the tab clears them.
• Ark trust model: off-chain sends are co-signed by the Ark server, which is the arbiter of off-chain spent/unspent state — but it can never spend your coins, and the pre-signed exit path means you can always return on-chain without its cooperation. Ark coins expire (weeks) if never refreshed; the wallet surfaces this, but don't park long-term savings in an Ark.
• Swap providers are non-custodial by protocol: worst case a swap fails and refunds on-chain.
• Whichever data source you query sees your addresses and IP — point it at your own node for full privacy. The localStorage cache and the Nostr event hold public chain data; the Nostr copy is encrypted end-to-end.