Heartwood Esp32 is free, open-source signer firmware for the Heltec WiFi LoRa 32 V3 and V4 boards. It is aimed at developers and technically confident Nostr and Lightning users who want signing keys kept on a small dedicated device instead of a general-purpose computer.
The design splits the work. The ESP32 handles all cryptography, while a Raspberry Pi running the heartwoodd bridge handles networking. The firmware also holds LNURLcash bearer notes, which can be sent and received as NIP-59 gift wraps. The latest release is v0.18.0-beta.29, so expect the project to change. Windows is mentioned in its documentation, but Windows support has not been verified in detail, so read the docs before you flash from a Windows PC.
What Heartwood Esp32 Is and Why It Exists
Heartwood Esp32 addresses a simple risk. Keys that sign Nostr events and Lightning-related actions are most exposed when they sit on a general-purpose computer that runs many programs and connects to many networks. The project moves those secrets onto a small Heltec board that has one main job.
The firmware is built as a signer, not as a wallet with a balance screen. It holds master secrets, prepares what each client needs, and returns signatures only when a request matches the policy you set. That narrow scope is intentional, because a smaller program has fewer ways to fail and fewer parts to audit.
The code is open source, so anyone with the skill can read how requests are handled and check the behavior against the source. That matters more for a signer than for most software, since the signing path is where a mistake costs the most.
How Work Is Split Between the Board and the Bridge
The system has two halves. The ESP32 handles decryption, signing and envelope construction. A Raspberry Pi running heartwoodd handles the networking, including connections to Nostr relays and the NIP-46 transport.
This split changes the threat model. If the Pi is compromised, an attacker still cannot pull a master key off the board or widen what a slot is allowed to sign. The limit is that an already authorized client can still receive any signature its current policy permits, so policy design matters as much as the hardware.
In practice, treat the policy as your main control. Keep slots narrow, review them after every change, and remove clients you no longer use. The hardware protects the keys, but the policy decides how those keys are used.
Who Should Consider a Hardware Signer for Lightning
Heartwood Esp32 suits people who already run Nostr or Lightning tools and want a signing device separate from their daily machine. A typical case is a developer who runs the bridge at home and keeps one board on a shelf, approving signatures for a small set of apps.
It is a weaker fit for someone who wants a simple mobile app to send payments on the go. Setup involves flashing firmware, running a companion server and managing tokens, which takes patience. Beginners who want a turnkey experience will find other catalog entries easier to start with.
If you do go this route, plan for the routine parts: a tested backup of your seed material, a written list of which clients have access, and a spare board in case the first one fails. Those habits matter more than any single feature.
Key features
On-device approval
Radios disabled in signer mode
Multiple master secrets
LNURLcash bearer notes
Browser management with Sapwood
Supported coins
The project documentation mentions Polygon and Nostr as networks, and lists Ledger among hardware wallets. Nostr is the protocol at the center of the signer's work, so most users will encounter it first.
How to install Heartwood Esp32 on Windows
- 1
Download from the official source
Open the project's GitHub repository, go to the Releases page and choose the build for your Heltec WiFi LoRa 32 V3 or V4 board. The latest release is v0.18.0-beta.29. Download only from the official website or GitHub, never from mirrors or forum links.
- 2
Verify the file
Compare the SHA-256 checksum or signature of the downloaded file with the values the project publishes. If the values do not match, delete the file and do not flash it.
- 3
Flash the firmware to the board
Connect the Heltec board over USB and flash the verified firmware using the steps in the project documentation. Windows is mentioned in the docs, but its support has not been verified in detail, so confirm the USB driver and flashing tool before you start.
-
Set up the Raspberry Pi bridge
Run heartwoodd on a Raspberry Pi to handle networking, then open the Management API on port 3100. Set a bearer token before you use the management interface, and keep the port off the public internet.
System requirements
- Heltec WiFi LoRa 32 V3 or V4 board
- Raspberry Pi running the heartwoodd bridge for networking
- Management API on port 3100, with a bearer token required except where the docs note otherwise
- Bare BIP-39 seed input; historical 24-word key backups remain supported
How to use Heartwood Esp32
Once the board and bridge are running, daily use comes down to approvals and policies. Start with one master and one client, then add more only after the first setup has proven stable.
- Load your master secret using bare BIP-39 input, which is the preferred format. Historical 24-word backups are still supported.
- Create a slot for one client and set its policy to the narrowest signing scope that client needs.
- Connect the client through the bridge and send a test request.
- Confirm the request on the board itself, and check that the result matches what you expected.
- Review the slot in Sapwood or through the Management API, and store the bearer token in a password manager.
- Add more clients or masters one at a time, testing each before moving on.
Pros & cons
- Keeps master secrets on a dedicated board, with radios disabled in signer mode
- Signing happens on the device, so a compromised bridge cannot extract master keys
- Supports several master modes, including bunker, tree-mnemonic and tree-nsec
- Free and open source, with the code available on GitHub for review
- Still in beta (v0.18.0-beta.29), so behavior may change between releases
- Requires a second machine, a Raspberry Pi bridge and firmware flashing
- Windows support is mentioned in the docs but has not been verified in detail
- Loose policies can still let an authorized client sign more than you intended
Is Heartwood Esp32 safe?
Heartwood Esp32 handles signing keys, so treat safety as the first step. Download only from the official website or the project's GitHub Releases page. Before flashing, verify the SHA-256 checksum or signature against the values the project publishes, and discard any file that does not match.
Never enter a seed phrase, master secret or bearer token on a third-party website, in a chat window, or in an app you did not install from an official source. Keep the Management API off the public internet and do not expose port 3100 to your home network without a clear reason. The project is in beta, so check the latest version on the official website before setting up a new board.
- Official source only. Download from github.com/forgesworn/heartwood-esp32. 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
Heartwood Esp32 is a signer, not a wallet, and that sets it apart from most entries in this category. Polar runs local Lightning networks in one click, which suits testing rather than holding keys. Peach is a desktop Lightning wallet for making small payments, where the software itself is the wallet. Spark Wallet offers a minimal interface for c-lightning across web, mobile and desktop. Zap Desktop is listed as no longer supported, so check its status before choosing it. If you need a device that signs for other software, Heartwood is the closer match. If you need a daily payment app, a wallet is the better fit.
Specifications
- Price
- Free
- Type
- Open source
- License
- —
- Latest version
- v0.18.0-beta.29
- Last update
- 28 Oct 2026
- Windows support
- Unverified (Windows mentioned in docs)
- Source code
- github.com/forgesworn/heartwood-esp32
Frequently asked questions
Yes, Heartwood Esp32 is free and open source. Its code is published on GitHub, so you can read it and compare it with the release you download. The firmware costs nothing, but the Heltec board and the Raspberry Pi running the bridge are separate hardware you would need to buy yourself.
It can be, if you set it up carefully. The main safeguard is design: master keys stay on the ESP32, and a compromised Pi cannot extract them. Risks remain in the setup, including loose policies, exposed management ports and phishing for seed phrases. Verify every download and keep each policy as narrow as possible.
Windows is mentioned in the project documentation, but its support has not been verified in detail. Read the docs before you flash from a Windows PC, and confirm that your USB driver and tools work with the Heltec board. A Linux machine may be the more predictable choice for flashing and running the bridge.
The firmware targets the Heltec WiFi LoRa 32 V3 and V4 boards. Other ESP32 boards are not part of the documented setup, so do not assume they will work. Check the project repository for any new hardware support before you order parts.
A bearer note is a token of value that whoever holds it can spend or redeem. Heartwood Esp32 can store these notes and send or receive them as NIP-59 gift wraps. Treat a bearer note like cash: once it leaves your control, it can be difficult to recover.
The project's design expects one. The Pi runs heartwoodd, which handles Nostr relays and NIP-46 transport, while the ESP32 does the cryptography. Without a bridge, the board has no path to the networking side of your setup, so plan for the second device from the start.
Verdict
Heartwood Esp32 is a focused, free signer for people who want Nostr and Lightning-related keys kept on a dedicated Heltec board. It fits developers and technically confident users who can flash firmware, run a Raspberry Pi bridge and maintain careful policies. It is not a casual payment app. Because it is still in beta, test with non-critical identities first and check the latest version on the official website before you commit.