03. Liquid SDK & Breeze - Deep Dive Summary
Core Thesis
Breeze’s mission is “Lightning in every app.” To achieve this, they have evolved from hosting virtual lightning nodes (Greenlight) to leveraging sidechains like Liquid and Spark. By abstracting the complexities of channel management and liquidity behind a simple “Connect-Prepare-Execute” paradigm, the Breeze SDK allows non-specialist developers to integrate non-custodial Bitcoin payments into any environment.
The Evolution of Breeze SDKs
Breeze provides Software Development Kits (SDKs) that hide thousands of lines of complex Rust code behind high-level interfaces.
- Greenlight (Legacy): The first iteration focused on running a native lightning node on mobile devices. It used hosted infrastructure by Blockstream but kept the private keys on the user’s device. It is now deprecated in favor of swap-based solutions.
- Liquid SDK (Active): Uses the Liquid Network (a sidechain) to trade liquidity between layers through swapping services like Boltz. It abstracts the “inner workings” of the two networks into a single interface.
- Spark SDK (Latest/2025): The newest implementation using the Spark network to allow even more fluid user experiences and instant Bitcoin transactions.
Part 1: The Developer Paradigm - Connect, Prepare, Execute
The Atomic Workflow
Breeze enforces a specific three-step logic for almost all operations to ensure flexibility and user safety:
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Connect: Initializes the SDK, syncs the blockchain, and starts background services (swap handlers, etc.).
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Prepare: Fetches fees, validates the destination, and identifies the swap cost before committing funds. This allows developers to show exact fees to users for confirmation.
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Execute: Performs the actual transaction (sending or receiving) using the data gathered in the preparation phase.
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Related Notes:
Part 2: Liquid vs. Spark Networks
Comparing the Layers
While the SDK interface remains nearly identical for both, the underlying networks have different trade-offs:
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Liquid Network: A federated sidechain with 1:1 BTC backing (L-BTC). It supports confidential transactions (privacy) and multi-asset payments (stablecoins, derivatives).
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Spark Network: A newer layer-two solution that prioritizes transaction speed and a smoother user experience, often bypassing some of the historical frictions found in channel-based lightning.
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Related Notes:
Part 3: Privacy & Non-Custodial Security
The Zero-Knowledge Approach
Despite using external services (like Boltz for swaps or Blockstream for Liquid), Breeze maintains a strict non-custodial model:
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Private Keys: Secrets and mnemonics are always stored only on the user’s device.
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Confidential Transactions: On Liquid, amounts and asset types are hidden from everyone except the participants.
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Trust Minimized: Swaps are atomic; if a provider goes offline, funds can be recovered via time-locks (Refund Flow).
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Related Notes:
Part 4: Advanced Features
Bridging the Ecosystem
The SDK isn’t just for payments; it includes “Quality of Life” bridges:
- Real-time Sync: Synchronizes metadata and payment history across devices using a (potentially self-hosted) cloud.
- Noster Wallet Connect (NWC): Allows remote control of the wallet from Noster apps (e.g., zapping people on social media).
- LNURL Support: Native handling of human-readable lightning requests for static QR codes.