Coin Selection Playground

Overview

Learning objectives

• Ship a working Coin Selection Playground that matches the description
• Cover the core skills: UTXOs, Algorithms, Fee math
• Document setup, demo steps, and known limitations in the README

Prerequisites

• UTXO Model
• Mempool & Fees

Part of the bitcoin roadmap.

Architecture diagram

app/          primary interface (CLI, API, or UI)
domain/       protocol and business logic
adapters/     Bitcoin Core, Lightning node, or indexer clients
tests/        smoke and regression coverage

Requirements

• Implements the stated goal: Implement largest-first and branch-and-bound style selection. Visualize waste, change, and fee tradeoffs on a fixed UTXO set.
• Runs against regtest, signet, or documented testnet endpoints (never assume mainnet funds)
• Includes a README with install, run, and demo instructions
• Has at least one automated test or scripted smoke check
• Fails safely with clear errors when dependencies are offline

Stretch goals

• Add a short architecture diagram to the README
• Publish a demo recording or asciinema session
• Compare two implementation approaches and note tradeoffs
• Add CI that runs the smoke test on every push

Recommended resources

• Mastering Bitcoin
• Bitcoin Optech
• Bitcoin Core RPC docs

Example repositories

• bitcoinjs-lib

  Transaction and address building in JavaScript.

• BDK

  Wallet toolkit used in production clients.

Submission instructions

• Public GitHub repository with a clear README
• Setup steps for local dependencies (regtest, Polar, Docker, etc.)
• Demo evidence (commands, screenshots, or short recording)
• Lab evidence pack: happy-path transcript + one intentional failure case + what error you saw
• Note difficulty assumptions and what you deliberately left out

Discussion