BOLT

BOLT - Basis Of Lightning Technology - is the specification series that defines how Lightning Network implementations interoperate. It's to Lightning what BIPs are to Bitcoin: a set of versioned, community-reviewed documents that anyone building Lightning software is expected to follow.

The current BOLT documents (numbered 0 through 12 with some experimental additions) cover:

• BOLT 1 - base protocol, message framing.
• BOLT 2 - peer protocol for channel management (open, close, update).
• BOLT 3 - transaction and script formats for on-chain channel state.
• BOLT 4 - onion routing (the Sphinx packet format).
• BOLT 5 - on-chain transactions and channel closure logic.
• BOLT 7 - gossip protocol for advertising channel info.
• BOLT 9 - feature flags.
• BOLT 11 - invoice format.
• BOLT 12 - offers (the reusable-invoice successor to BOLT 11), merged 2024.

Maintained on github.com/lightning/bolts by representatives of the major implementations - Lightning Labs (LND), Blockstream (Core Lightning), ACINQ (Eclair), Spiral (LDK). Changes go through pull requests, review, and broad consensus across implementations.

This multi-vendor coordination is why a Phoenix wallet (Eclair) can open a channel with a Core Lightning node and route through LND-operated infrastructure to pay an LDK-based receiver. They all follow the same BOLTs.