A zero-trust Ethereum transaction broadcaster. Paste a raw signed hex, verify every detail, and push — entirely in your browser.
ColdCast is built for one thing: broadcasting already-signed Ethereum transactions without ever putting your private key online.
The workflow is exactly three steps:
① Paste signed hex → ② Inspect & verify → ③ Broadcast
Sign your transaction on an air-gapped device or hardware wallet, bring the hex across (or scan the QR), confirm the decoded details look right, and broadcast. Done.
| 🔍 Full Decode | Sender, recipient, value, nonce, gas, chain ID, signature validity |
| 🪙 ERC-20 Detection | Auto-identifies token transfers — shows token, amount & recipient |
| ⚡ EIP-1559 Support | Handles both legacy and type-2 transactions |
| 📷 QR Scanner | Reads signed hex from your camera or a gallery image |
| 🌐 Multiple RPCs | PublicNode, LlamaRPC, Flashbots, or any custom endpoint |
| 💹 Live Prices | Real-time ETH/USD price & gas tracker in the header |
| 📱 Mobile Ready | Fully responsive, touch-optimised |
| 🔒 Zero Exposure | No keys, no server, no analytics — nothing leaves your browser |
ColdCast makes exactly one outbound request: the RPC call you trigger yourself to broadcast the transaction.
- No backend
- No telemetry
- No wallet connection
- No private key input, ever
The entire app is a single auditable .html file. Read it. All transaction parsing happens locally via ethers.js v5.
Download and open — no install required.
git clone https://github.com/th3proton/ColdCast.git
open ColdCastSigner.htmlOr visit coldcast.app — same file, served statically.
Built with zero dependencies beyond what's loaded from CDN at runtime:
- ethers.js v5 — transaction parsing & RPC broadcast
- jsQR — QR code scanning
- QRCode.js — donation QR generation
- Vanilla HTML / CSS / JS — no framework, no build step
If ColdCast saved you from pasting your seed phrase into a sketchy site, consider buying me a coffee.
ETH Donation Address:
0x1337b9946966662e32De7394989eb43D8B28f90D
EVM mainnets only. ETH/BNB/POL ....The address is also shown with a scannable QR code inside the app.
The entire app is ColdCastSigner.html. Fork, edit, test in a browser, open a PR.
⚠️ On-chain transactions are irreversible. Always verify the decoded details before hitting broadcast.
MIT License · coldcast.app · Made with ♥ for cold wallet users