Ledgerline

Build a web app called Ledgerline: invoices for freelancers that chase themselves.

What it does

Create an invoice in under a minute, send it, and let Ledgerline follow up politely when it's late. The reminders get firmer over time, in a tone you choose.

Stack

Use Next.js, Stripe, Postgres, Vercel. The original was built with v0 and Claude Code in 1 month, for about $75 in AI usage.

How it fits together

• A server-rendered web app with a small API layer
• A database for user data, with row level security on every table
• Sign-in so each person only sees their own data

Build it in this order

1. Set up the project, the database and sign-in, and deploy an empty page
2. Build the main screen with realistic sample data
3. Connect it to real data and add the one action the app exists for
4. Add the empty states and error messages a new user will hit
5. Write tests for anything that touches money, dates or other people's data

Tools to connect

• Stripe MCP: products, prices and webhooks set up by the agent

A prompt that worked: Reminder emails that get firmer

Write four reminder emails for an unpaid invoice: 3 days late, 10 days, 21 days and 35 days. Each one slightly firmer than the last, never rude. Keep each under 80 words. Use {client_name}, {invoice_number}, {amount} and {due_date}. Then write the same four in a ‘very friendly’ tone.

Watch out for

• Don't build settings, teams or billing before the main screen works
• Keep the first screen useful with sample data, so the app makes sense before anyone has set it up

Done when

• A new user can sign in and get value in under two minutes
• Everything works on a phone
• Tests pass for the core logic

Before writing code, ask me up to five questions about who this finance web app is for and what the first version must do. Then work in small steps: after each one, tell me how to try it and wait for my feedback.