Core Lightning

Core Lightning (CLN) emphasizes modularity: a lean daemon extended by plugins. It frequently ships cutting-edge protocol features early.

Why this matters

If you need custom RPC behavior or want to experiment with offers/splicing, CLN’s plugin system is a powerful builder surface.

lightning-cli getinfo
lightning-cli invoice 100000 "label" "desc"

Worked mental model

Re-read the diagrams in this lesson once out loud in plain language. If you cannot explain the flow to a friend without jargon, pause and revisit Mastering Bitcoin / Mastering Lightning chapters linked in Resources. Chapter references are intentional, not decorative.

Hands-on habit

Every protocol idea should be paired with one local experiment:

1. Reproduce the happy path on regtest (or Polar for Lightning)
2. Break it on purpose (wrong fee, expired invoice, offline peer)
3. Write down what error you saw and which layer produced it (wallet, node, mempool, peer)

That habit turns reading into builder instinct.

Glossary check

Pick three terms from this lesson and define them in one sentence each without opening notes. Weak definitions mean the lesson is not finished yet.

Resource order

Use Resources in order: narrative book chapter first, then BIP/BOLT for precision, then implementation docs for commands. Jumping straight to RPC flags without the mental model creates brittle knowledge.

Next steps

LDK, embed Lightning directly into applications.