Bitcoin Custody Tools (Free)

Bitcoin Custody Tools · Frozen Security FROZEN SECURITY / TOOLS Bitcoin Custody Tools Browser-based utilities for constructing, inspecting, and broadcasting Bitcoin transactions. All computation runs client-side. No keys, seeds, or transaction data leave your device. Entropy Generator Generate cryptographically secure BIP-39 mnemonics using the browser's native CSPRNG. Displays raw entropy bits, checksum derivation, and per-word bit mapping. Nothing is transmitted or stored. Input Entropy strength Output Mnemonic, entropy and bit structure BIP-39 CSPRNG Checksum Seed Visualizer Converts each word of a BIP-39 mnemonic into its 11-bit wordlist index. Rendered as a binary position grid — the same structure used in a physical hole-pattern encoding. Input 12 or 24-word mnemonic Output Binary grid + bit string BIP-39 11-bit Entropy Checksum Hole Pattern Decoder Toggle 11 bit positions to decode a physical hole pattern into its BIP-39 word. Works in both directions — type a word to illuminate its pattern. Add rows to reconstruct a full mnemonic. Input Bit pattern or word Output Word / pattern BIP-39 Physical key Recovery Bidirectional UTXO Lookup Fetch unspent outputs for a Bitcoin address from mempool.space. Select UTXOs and copy them directly into the PSBT Builder — completing the full custody workflow. Input Bitcoin address Output Selectable UTXO list Mainnet Testnet Signet mempool.space Fee Estimator Estimate Bitcoin transaction size and fee from input and output composition. Live fee rates fetched from mempool.space. All calculation runs in the browser. Input Fee rate, inputs and outputs Output Estimated size and fee Fee CSPRNG Checksum PSBT — BIP-174 What is a Partially Signed Bitcoin Transaction? BIP-174 defines the Partially Signed Bitcoin Transaction format. A PSBT separates transaction construction from transaction signing. An online computer builds the unsigned transaction; an offline signer performs the cryptographic operation; the signed result is returned for broadcast. PSBT is the natural interface layer for physically governed custody. The unsigned transaction travels to the signing primitive; the private key is derived transiently for signing; only the signed output leaves the device. No key material crosses the air gap. MNEMONIC — BIP-39 How BIP-39 encodes entropy as words BIP-39 encodes cryptographic entropy as a sequence of words from a standardized 2048-word list. Each word corresponds to an 11-bit integer (0–2047). The full word sequence represents a binary string from which a deterministic wallet seed is derived via PBKDF2. The seed visualizer renders each word as its 11 binary positions — the same representation used in a physical hole-pattern encoding. This makes the information structure of a mnemonic directly inspectable. SECURITY NOTICE All operations on this page run in the browser. No data is transmitted to Frozen Security servers. The PSBT broadcaster communicates directly with the mempool.space public API to submit signed transactions. Do not use these tools on compromised devices or unsecured networks when handling live transaction data.