# GapFix

> Free, open-source Bitcoin HD wallet gap limit recovery tool. Paste your xpub/ypub/zpub to find and fix Bitcoin stuck beyond the 20-address gap limit — no private keys required, runs entirely in your browser.

## What is GapFix?

GapFix (gapfix.net) solves the Bitcoin address gap limit problem. Bitcoin HD wallets stop scanning after 20 consecutive empty addresses. If funds were sent to an address beyond that gap, the wallet shows a zero balance even though the Bitcoin exists on-chain. GapFix scans up to 1,000 external and 1,000 change addresses to find those hidden UTXOs and explains how to recover them.

## Key Concepts

- **Bitcoin gap limit**: The default limit of 20 consecutive empty addresses that HD wallets scan before stopping. Defined in BIP-44.
- **xpub / ypub / zpub**: Extended public keys for legacy (P2PKH), segwit-wrapped (P2SH-P2WPKH), and native segwit (P2WPKH/bech32) wallets respectively.
- **UTXO recovery**: Unspent transaction outputs that exist on-chain but are invisible to the wallet because they sit beyond the gap limit.
- **Dust fix**: Send a small amount (294–546 satoshis) to empty addresses inside the gap so the wallet scanner continues past them and discovers the hidden funds.

## How Recovery Works

1. Paste your account-level xpub, ypub, or zpub into GapFix.
2. GapFix derives up to 2,000 addresses (1,000 external + 1,000 change) in-browser.
3. Each address is checked against Blockstream's public API for transactions and balances.
4. GapFix identifies gap addresses (empty addresses before a funded address) and shows you which ones need dust transactions.
5. Send dust (minimum non-dust amount per address type) to the gap addresses — your wallet will then rescan and show the full balance.

## Target Use Cases

- Bitcoin is missing from wallet after seed import or wallet migration
- Wallet shows zero balance after restoring from seed phrase
- Exchange or app sent Bitcoin to an address beyond index 20
- Non-standard derivation path caused addresses to be skipped
- Recovering Bitcoin from old wallets with many receive addresses generated

## Technical Details

- Supports BIP32, BIP44, BIP49, BIP84 HD wallets
- Compatible with Ledger, Trezor, Coldcard, BitBox, Electrum, Sparrow, Wasabi
- Minimum dust amounts: 294 sats (bech32/bc1q), 546 sats (legacy/P2PKH, segwit-wrapped/P2SH)
- All computation is client-side; only public addresses are queried externally
- Open source: https://github.com/matrenitski/gapfix.net

## Documentation

- [Full tool documentation](https://gapfix.net/llms-full.txt)
- [GitHub repository](https://github.com/matrenitski/gapfix.net)