What Trezor Bridge is and why it matters
Trezor Bridge is a small helper application that runs on your computer and exposes a secure, local communication channel between a web browser and a Trezor hardware wallet. Modern browsers place strict sandboxing and security limits on web pages; Bridge bridges (pun intended) that gap by listening on a loopback (localhost) port and proxying messages from a website (or desktop app) to your physical Trezor. That local relay allows the hardware device to remain the authoritative signer for private keys while letting user interfaces in the browser ask the device to confirm addresses, sign transactions, or export public keys — all without revealing private keys outside the device.
Bridge is intentionally minimal in scope: it does not store your seeds or keys, it only provides a communication path and optional device metadata. The design keeps the cryptographic surface area small while allowing developers to build rich, browser-based wallet interfaces that still rely on an isolated signing environment. Because the connection is local and ephemeral, typical remote attacker vectors (like a remote web server directly injecting commands) are mitigated — the user must physically confirm actions on the Trezor device itself.
How it works — a high-level flow
In simple terms, the flow looks like: user opens a wallet web page → web page requests to enumerate connected devices via Bridge's local API → Bridge returns a list of attached devices → the page sends a signing request to Bridge → Bridge forwards that request to the device over USB (or WebUSB where supported) → the device prompts the user to confirm the action on its screen → once approved, the device returns the signature to Bridge → Bridge returns it to the web page. Because the approval step happens on the device, even if a compromised page asks for a transaction, the attacker cannot bypass the physical confirmation step.
Bridge also handles device firmware compatibility, implements timeouts, and often exposes a small, versioned JSON API so that multiple front-end projects can use the same underlying connectivity layer. The app commonly auto-updates or prompts the user when a new Bridge release becomes available — maintaining compatibility as browsers and OSes evolve.
Installation & platform notes
Bridge is distributed for Windows, macOS and Linux. On most systems it runs as a background helper or service and installs with a lightweight installer. Because Bridge listens only on loopback (127.0.0.1) and uses OS-level USB driver bridges, it intentionally never exposes a remote API. When installing, prefer official downloads from the hardware vendor's site or verified package repositories. On macOS, installation may require permission to allow network (localhost) traffic; on Linux, running udev rules may be needed so non-root users can access USB devices.
From a privacy perspective, Bridge does not need internet access to function. If asked by the user interface, the device will only sign actions you approve. Keep an eye on operating system warnings during install and avoid unofficial third-party builds unless you understand the provenance.
Troubleshooting common issues
If a website cannot see your Trezor, verify these basics: is Bridge running? (system tray or background process), is the device unlocked and connected, and is the USB cable/data line healthy? Try switching USB ports (preferably directly into the computer rather than via a hub). On some platforms, browser permissions may block access to the loopback API — restarting the browser or toggling permissions often helps. If Bridge fails after an OS update, reinstalling the latest Bridge build usually fixes compatibility breaks. Finally, consult vendor-provided logs (or Bridge's diagnostic window) for verbose error messages; they often hint whether the issue is a driver, permission, or firmware mismatch.
Security best practices
A few practical recommendations enhance security when using Bridge with a hardware wallet: (1) Keep device firmware up to date only from the official vendor channel. (2) Only use Bridge downloads from the vendor website. (3) Never enter your recovery seed into a browser or a computer — recovery must remain offline. (4) Use a dedicated, well-audited browser profile for wallet interactions to reduce the risk of cross-site contamination. (5) When prompted on the device, read the exact transaction details on the device's screen; never blindly approve prompts. These simple habits reduce risk and keep the device's isolating guarantees intact.
Developer notes & automation
For developers, Bridge exposes a stable JSON-RPC-like API for enumerating devices and forwarding APDU-like messages to the hardware. Most SDKs abstract this complexity and provide convenient methods to request signatures or query public keys. When scripting or integrating Bridge into CI workflows, avoid storing secrets on automation servers; use test-only keys and ensure human confirmation for any sensitive operations. Bridge can be mocked in unit tests so that UI code can be exercised without a physical device.
Final thoughts
Bridge is a pragmatic engineering compromise: it preserves the security guarantees of a hardware wallet while enabling modern, web-driven user experiences. Its role is narrow but essential — and when paired with cautious user behavior and vendor-sourced software, it offers one of the most accessible paths to robust private-key security. This page intentionally avoids login or account UI elements; Bridge's purpose is local device connectivity and not user authentication. If you experiment with Bridge, treat it as a system-level helper: keep it up to date, monitor permissions, and always confirm actions on the physical device.