Olesia.

A Bitcoin wallet built from scratch on audited primitives — cold generation, honest entropy, and a testnet playground you can actually use.

Open the wallet →

Send, receive, sweep and message on testnet. Balances, QR, history. Runs in your browser.

app.olesia.io

Cold generator →

Create a 24-word seed, backup and watch-only descriptor. Built to run offline.

offline.olesia.io

The one rule. For any wallet you will fund with real value: download the cold generator, verify its hash (below), disconnect from the internet, and run it offline. A page served over the web can be changed by whoever controls the server — verifying the hash and running offline removes that trust. The online wallet is for testnet and small amounts.

Verify the cold generator

The build is byte-reproducible. Confirm any copy you download is exactly the reviewed code:

curl -sL https://offline.olesia.io -o olesia.html
sha256sum olesia.html
# expected:
8a28ce4a92cf421bd332fbffd053fbddb6ea18b76d1eab255d7039285ac3a668

Full instructions and an independent Sparrow round-trip are in VERIFY.md. Source, security audit and reproducible build: github.com/testnetbtc/BTC_Wallet.

How it's built

Cold generator — audited @scure/@noble primitives, 256-bit entropy from the OS CSPRNG, fail-closed self-check, encrypted authenticated backups, reproducible single-file build.
Online wallet — signs locally with @scure/btc-signer (RFC-6979); balances/broadcast over the network; never stores your seed.
Mainnet (coming) — air-gap only: watch-only online, sign offline, broadcast through your own node. The seed never goes online.

Olesia is experimental and self-audited. Not financial advice; not a substitute for a hardware wallet for large sums. Testnet first, always.