BTC Airgap Bridge is a free, open-source browser tool for people who keep their Bitcoin in an air-gapped setup and want to go online only when it is necessary. It helps you fetch live network data such as UTXOs and fee rates, then broadcast a signed transaction to the Bitcoin network, all without exposing your private keys to an internet-connected machine. If you are looking at BTC Airgap Bridge for Windows, this page explains what the tool does, what it leaves to you, and how to use it carefully.
The project is released under the Apache 2.0 license and runs entirely on the client side, so your data is not routed through a server of its own. Its code was last updated in July 2025, which places it among projects that have been maintained fairly recently. Windows appears among the platforms named in the documentation, but because the tool ships as a single HTML file, most people will use it through a browser on a Windows PC.
What Is an Air-Gapped Bitcoin Workflow?
An air-gapped setup keeps a signing device physically separate from any network. The machine that holds your private keys never connects to the internet, Wi-Fi, or a local network, so malware on an online computer has no direct path to those keys. The approach is common among people who hold Bitcoin for the long term and want to lower the risk of remote theft.
The trade-off is practical. A transaction needs current information to be built correctly: you must know which unspent outputs you can spend, and you need a sensible fee rate for the moment you send. That data lives on the network, so someone has to fetch it. Broadcasting then requires the signed transaction to reach the network. This is the gap that tools like BTC Airgap Bridge are designed to fill.
Consider a simple case. You keep a modest balance in a cold wallet on an offline laptop and want to pay an invoice. You go online briefly on your Windows desktop, fetch the data, carry it to the laptop by QR code, sign there, and return only the signed hex. The online machine never handles the key, and the signed transaction does not reveal it.
Who Is BTC Airgap Bridge For?
BTC Airgap Bridge suits people who already run an offline signing process and want a focused tool for the online half. A typical reader keeps keys on a dedicated machine, understands what a UTXO is, and is comfortable checking transaction details before submitting anything. Privacy-minded holders and people who manage Bitcoin for a small business often fall into this group.
It is less suitable for beginners who expect a one-click app that manages balances, contacts and transaction history. The tool does not aim to do that, and the documentation focuses on Bitcoin only. If you need several cryptocurrencies in one place, a multi-currency wallet from this catalog is a better starting point.
For example, a freelancer who receives Bitcoin payments might use the tool once or twice a month: fetch current fee rates when paying a supplier, move the transaction through QR codes, and submit it. The routine is slower than a standard wallet, and that is the point. Each extra step is a chance to double-check the details before money moves.
Why UTXOs and Fee Rates Matter Before Signing
Bitcoin balances are not stored as a single running number. Funds sit in unspent transaction outputs, usually called UTXOs, and a transaction spends one or more of them. Knowing which outputs are available, and which combination makes sense for a payment, is the first thing an offline signer needs. Stale data can lead to a rejected transaction or an unexpected change output, so fetching the list close to the time of signing is good practice.
Fee rates work in a similar way. Miners tend to prioritize transactions that pay more per unit of data, so the recommended rate reflects current demand on the network. Paying well below it may leave a transaction waiting for a long time, while overpaying only reduces your own balance. A fresh rate lets you choose a sensible figure instead of guessing.
The Fetch UTXOs and Fees step is therefore the most important function in this workflow. Run it immediately before you move data offline, and assume that the figures will change as the network moves.
Key features
Fetch UTXOs and Fees
Submit Signed Transaction
Generate QR Code
Regenerate QR Code
Supported coins
The documentation names Bitcoin (BTC) as the network this tool works with, and its workflow is built around Bitcoin's UTXO model and fee market. The project also lists SHA-256 as the mining algorithm associated with Bitcoin. That detail describes the network rather than a feature of the tool, which does not mine. If you need support for other networks, look at the multi-currency wallets elsewhere in this catalog.
How to install BTC Airgap Bridge on Windows
- 1
Get the file from the official source
Download only from the official website or the project's GitHub Releases page at github.com/paranoid-qrypto/btc-airgap-bridge. Avoid copies shared on forums, chat groups or file-sharing sites, since a modified HTML file could capture the data you enter into it.
- 2
Check the file before opening it
Compare the SHA-256 checksum of the downloaded file with the value published by the project. If a signature is provided, verify it as well. Do this on the internet-connected computer before you open the file for the first time.
- 3
Save the file in a dedicated folder
Keep the file in a folder you control and give it a clear name so you remember it belongs to the online side of your workflow. Because the program is a single HTML file, there is no traditional installer. The file itself is the program.
-
Open it in a browser on Windows
Double-click the file to open it in your default browser, or drag it into an open browser window. Confirm that your internet connection works, because fetching UTXOs and fee rates and broadcasting a transaction both require it.
System requirements
- An internet connection, needed to fetch UTXOs and fee rates and to broadcast signed transactions
- A web browser on Windows to open the single-file HTML tool
How to use BTC Airgap Bridge
BTC Airgap Bridge sits on the online side of an air-gapped transaction. Your signing happens on a machine that never connects to the internet, and the tool handles the steps that need network data. Follow the sequence below and keep the offline device disconnected from every network at each stage.
- On the online device, open the tool and use Fetch UTXOs & Fees to retrieve your unspent outputs and the current recommended fee rates.
- Use Generate QR Code to turn the data your offline device needs into a scannable image, then display it on screen.
- On the air-gapped machine, scan or paste that data and build the transaction in your offline wallet. Sign it there, so the private key never leaves that device.
- Move the signed transaction hex back to the online device, either by scanning a QR code or by copying the text.
- Use Submit Signed TX to broadcast the transaction to the Bitcoin network. Review the hex and the amounts before you submit, because a broadcast cannot be reversed.
- If a QR code is blurry or hard to read, run Regenerate QR Code to produce a clean copy, then try the scan again.
Pros & cons
- Free to use and released under the Apache 2.0 open-source license
- Keeps private keys away from internet-connected machines
- Fetches UTXOs and fee rates before signing, which reduces guesswork
- QR tools move signed transactions across the air gap without file copies
- Source code is public on GitHub for anyone who wants to review it
- Only Bitcoin (BTC) is named in the documentation
- Requires an internet connection for fetching data and broadcasting
- Windows is mentioned in the documentation, but the tool is a browser file rather than a dedicated Windows application
- The workflow has many manual steps and is slower than a standard wallet
- It is not a full wallet and does not manage balances or history
Is BTC Airgap Bridge safe?
Download BTC Airgap Bridge only from the official website or the project's GitHub repository, and avoid copies offered on forums, unknown app sites, or file-sharing services. Before running the file, compare its SHA-256 checksum with the value published by the project, or verify a signature if one is provided. The tool is built so that private keys never reach an internet-connected device, but that design only helps if your signing machine stays truly offline. Never enter a seed phrase or private key into any website, including one that imitates this tool's page. Check the latest version on the official website before using it with real funds.
- Official source only. Download from github.com/paranoid-qrypto/btc-airgap-bridge. Ignore ads and lookalike domains.
- Check the SHA-256. Compare the installer hash with the value the developer publishes before running it.
- Never share your seed phrase. No developer, support agent or website — including CryptApps — will ever ask for it.
Alternatives
Electrum is a lightweight Bitcoin wallet with Lightning support, multisig and hardware wallet integration, so it covers far more ground than BTC Airgap Bridge. Sparrow Wallet targets advanced users with multisig and coin control, and Armory is built around cold storage. Wasabi Wallet focuses on privacy through CoinJoin. BTC Airgap Bridge does a narrower job: it handles the online half of an air-gapped transaction and leaves the wallet itself to other software. If you want a complete wallet, start with one of those options. If you already have an offline signing setup and only need a clean way to fetch data and broadcast, this tool fills that gap.
Specifications
- Price
- Free
- Type
- Open source
- License
- Apache 2.0
- Latest version
- —
- Last update
- 3 Jul 2025
- Windows support
- Unverified (Windows mentioned in docs)
- Source code
- github.com/paranoid-qrypto/btc-airgap-bridge
Frequently asked questions
Yes, BTC Airgap Bridge is free and is distributed under the Apache 2.0 open-source license. You can read its source code on GitHub, which lets technically minded users check how it fetches data and builds requests. Free software still leaves responsibility with you, because the security of your Bitcoin depends on how you handle the offline device and each transfer step.
It is designed to keep private keys off internet-connected devices, which is the main safety goal of an air-gapped workflow. Safety still depends on where you got the file, whether you checked its checksum, and whether your signing machine stays offline. Read the safety section on this page before using the tool with real funds.
No. The tool is built so that private keys never leave an offline machine, and the online side only handles public data such as UTXOs, fee rates and a signed transaction hex. Never paste a seed phrase or private key into any browser tool, including this one, because a signed transaction is all the online side should ever need.
Windows is among the platforms named in the project documentation. Because the tool is a single HTML file, you run it in a modern web browser on Windows, and the same file can be opened on other systems. Test the full workflow with a small amount before relying on it for larger transfers.
The documentation mentions Bitcoin (BTC) only. The tool is built around Bitcoin's UTXO model and fee rates, so it is not a multi-coin wallet. If you hold other cryptocurrencies, you will need separate software for those transactions.
Start by fetching UTXOs and fee rates on the online device, then move that information to your offline signing setup using QR codes. After you sign the transaction offline, bring the raw hex back to the online device and submit it. The how-to section on this page walks through the sequence step by step.
Alternatives depend on whether you need a full wallet or only the online broadcast step. Electrum, Sparrow Wallet and Armory are Bitcoin wallets with offline or cold-storage features, while Wasabi Wallet focuses on privacy through CoinJoin. The comparison section above explains how they differ from this tool.
Verdict
BTC Airgap Bridge is a focused, free tool for experienced Bitcoin holders who already keep their keys on an offline device and want a safer way to go online briefly. It does not store funds, does not cover other coins, and is not a replacement for a full wallet. Treat it as one part of a careful process, test the workflow with small amounts first, and keep your seed phrase offline at all times. If that routine suits you, BTC Airgap Bridge for Windows is a clear option for the online steps.