Bitcoin for Builders Build and contribute

Project: ship a small Lightning or Fedimint tool

Your capstone. Pick a brief, build it on regtest or a mock, publish it as open source, and get it reviewed by the Bitsacco community.

600 minIntermediate8 / 8

Draft: this lesson is still waiting for review.

What you'll learn

Plan, build and test a small Bitcoin tool from a written brief
Publish it as open source with a README in Kiswahili and English
Present it to the community and act on a reviewer's feedback

Key terms

regtest: A private Bitcoin test network you control, where blocks are mined instantly.
Lightning Network (mtandao wa Lightning): A network on top of Bitcoin for fast payments with very small fees.
open source (programu huria): Software whose code anyone can read, check and improve.

This is where the path comes together: a small, real tool, built in public and reviewed by people who will use it. Plan for about two weeks of evenings. A finished small tool beats an unfinished big one.

Step 1: Pick a brief

Brief	What it does	Builds on
Chama tip jar	The mini-app from lesson 6, finished: amount buttons, QR invoices, Kiswahili and English, error messages in plain words	Lightning Address, LNURL-pay
UTXO explainer	A command-line tool that lists a regtest wallet's UTXOs and explains, in plain language, which would be spent for a given payment and what the change would be	UTXOs, RPC
Offline sats calculator	A page that converts shillings to sats and back from a price the user types in, works offline, and shows the volatility warning from the savers path	PWA, sats
Federation guide	A step-by-step guide, with diagrams, for a chama running a test Fedimint federation on regtest, in both languages	Fedimint

You may propose your own, as long as it fits the rules below.

Step 2: Rules

Runs on regtest, signet or a mock only. No real funds, no real seed phrases.
Never asks for, stores or transmits a seed phrase or private key.
Published as open source with a licence (MIT or similar) and a README in Kiswahili and English.
Has automated tests for its core logic, and they run in CI.

Step 3: Build in small steps

Write a one-paragraph plan in the README: who it's for, what it does, what it won't do.
Build the smallest version that works end to end.
Add tests, then the second language, then polish.
Ask a friend who has never seen it to use it on their phone. Watch, don't help, and write down where they got stuck.

Done when

The README explains the tool in Kiswahili and English, with setup steps that work on a fresh machine.
Tests pass in CI.
It works on a phone-sized screen, or in a terminal 80 columns wide for CLI tools.
Someone else has used it from the README alone.
Your lab evidence from lessons 1 to 6 is linked, showing the skills you built on.

Lab evidence

The link to your repository and its passing CI run.
Your reviewer's feedback and the commits where you acted on it.
A two-minute screen recording or a short written walk-through.

Reflect

Write your answer down, or talk it over with a friend or your chama.

What did you cut from your first plan, and why?
What did your reviewer notice that you had missed?