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BOLT | Bitcoin Glossary | Mapping Bitcoin

BOLT

Lightning

Also known as: Basis of Lightning Technology, BOLT spec

Basis of Lightning Technology, the set of specifications that define the Lightning Network protocol. BOLTs describe the rules for opening and closing channels, routing payments, encoding invoices, and other aspects of Lightning interoperability.

Overview

BOLTs (Basis of Lightning Technology) are the technical specification documents that define how the Lightning Network operates. Similar to how RFCs define internet protocols, BOLTs ensure that different Lightning implementations (LND, CLN, Eclair, LDK) can interoperate seamlessly. The specifications are developed collaboratively and maintained on GitHub.

BOLT Specifications

BOLT #   Title                              Purpose
──────────────────────────────────────────────────────────────────
  1      Base Protocol                      Messaging and connection
  2      Peer Protocol for Channel Mgmt     Opening/closing channels
  3      Bitcoin Transaction and Script     On-chain transaction formats
  4      Onion Routing Protocol             Payment routing privacy
  5      Recommendations for On-chain TX    Fee handling and policies
  7      P2P Node and Channel Discovery     Network gossip protocol
  8      Transport and Authentication       Encrypted communication
  9      Assigned Feature Flags             Capability advertisement
 11      Invoice Protocol for Payments      Payment request encoding

Why Interoperability Matters

The Lightning Network's value depends on all participants being able to transact with each other regardless of which software implementation they use. BOLTs provide the common language that makes this possible. A payment initiated from an LND node can route through CLN nodes and arrive at an Eclair node without any compatibility issues, because all implementations follow the same BOLTs.

Evolution

BOLTs are living documents that evolve as the Lightning Network matures. Proposed changes are discussed among implementation teams, tested for compatibility, and formally adopted when consensus is reached. Recent additions include specifications for offers (BOLT12), which improve upon the original invoice format with features like reusable payment codes and payer privacy.

Common Misconceptions

BOLTs define the protocol, not the implementation. Each Lightning implementation (LND, CLN, Eclair, LDK) is free to organize its code and add features as it sees fit, as long as it adheres to the BOLT specifications for cross-implementation communication.

Related Terms

Lightning NetworkLightning

A Layer 2 payment protocol built on top of Bitcoin that enables instant, low-cost transactions through a network of bidirectional payment channels. Payments are routed through multiple channels using HTLCs, settling on the Bitcoin blockchain only when channels are opened or closed.

Lightning ChannelLightning

A two-party payment channel on the Lightning Network created by locking bitcoin in a 2-of-2 multisig on-chain transaction. Once open, the channel allows the two parties to make unlimited fast, low-cost payments between each other off-chain.

HTLCLightning

Hash Time-Locked Contract, a conditional payment mechanism used in the Lightning Network and atomic swaps. An HTLC locks funds that can only be claimed by providing a cryptographic preimage before a timeout expires, enabling trustless multi-hop payments.

Routing (Lightning)Lightning

The process of finding a path through the Lightning Network's graph of payment channels to deliver a payment from sender to recipient. Routing nodes forward payments and can earn small fees for providing this service.