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name: bitcoin-testing-polar description: | Polar: GUI for spinning up Lightning regtest networks. Supports LND, Core Lightning, Eclair, plus Lightning Terminal (litd) and Taproot Assets. Per-node config, payment simulation, channel topology editor, sim-ln activity, MCP server for AI agents. USE WHEN: building / testing Lightning apps, designing regtest channel topologies, demoing LN flows. allowed-tools: Read, Grep, Glob

Polar

Lightning Network regtest GUI. One-click setup of multi-node LN networks for testing.

Repo: github.com/jamaljsr/polar.

Features

• Multi-node: bitcoind + LND / Core Lightning / Eclair, plus Lightning Terminal (litd) and Tap (Taproot Assets). Polar ships no LDK / LDK Node image (checked against Polar v4.0.0, January 2026).
• GUI: drag-and-drop network builder.
• Channel topology editor: open / close channels visually.
• Payment simulator: send/receive between nodes.
• Balance + fee customization.
• Persisted networks: save/restore.
• Tor optional for testing onion-only setups.
• sim-ln activity (Polar 4.0.0, 6 January 2026): activity rules of source / destination / amount / interval drive continuous payments across the network, via bitcoin-dev-project/sim-ln.
• MCP server (Polar 4.0.0, 6 January 2026): 48 tools exposed to Claude Code / Cursor / Codex over the @lightningpolar/mcp stdio server, which talks to Polar's HTTP bridge on localhost:37373.

Supported images

Version ranges as shipped in Polar 4.0.0 (docker/nodes.json, read September 2026):

Node	Versions
LND	0.16.4 - 0.20.0 (beta tags)
Core Lightning	24.08.1 - 25.12
Eclair	0.9.0 - 0.13.1
Bitcoin Core	26.0 - 30.0
Taproot Assets	0.3.3 - 0.7.0 (alpha tags)
Terminal (litd)	0.14.1 - 0.16.0 (alpha tags)

nodes.json also carries a compatibility map: LND 0.18.4+ pairs with bitcoind 30.0, LND 0.18.3 and older with 27.0. Custom images (master branch, local fork) are added via Polar's custom-nodes flow.

Setup

Download installer (Mac/Win/Linux). Requires Docker.

Create network:

1. New network → name + chain (regtest).
2. Drag node icons (LND, CLN, etc.) onto canvas.
3. Add bitcoind backend.
4. Start network.
5. Open channels via UI.
6. Send payments.

Use cases

• Lightning app development: test against real LND/CLN APIs.
• Multisig coordinator testing across LN-aware impls.
• Demos for tutorials, presentations.
• Education: visualize LN flows.

Compared

Aspect	Polar	Nigiri	Manual regtest
GUI	yes	no	no
Multi-LN-impl	LND / CLN / Eclair (+ litd, tapd)	LND + CLN (+ tapd)	yes
Esplora explorer	no	yes	manual
Use case	LN focus	Bitcoin focus	Custom

Nigiri column as of Nigiri v0.5.17 (May 2026): nigiri start --ln brings up Core Lightning, LND and the Taproot Assets daemon together, not LND alone. It ships no Eclair image.

Common issues

• Docker required and runs containers; resource-heavy on small machines.
• Port conflicts with existing services.
• Old saved networks may break across Polar versions; export node configs separately for portability.

See also

• regtest/SKILL.md
• nigiri/SKILL.md
• signet/SKILL.md
• ../lightning/lnd/SKILL.md
• ../lightning/cln/SKILL.md