Costwatch

Know what your product actually costs.

Track product costs, revenue, renewals, and profit in one place.

The problem

Your side project or small SaaS probably has a hosting bill, a database, an API or two, a domain, email, design tools and a few other subscriptions. Individually they look small. Together they're your operating cost, and they're spread across a dozen dashboards, invoices and card statements.

Most developers know roughly what their product earns. Few can say what it costs to run. Costwatch gives you one place to answer:

• What am I paying for?
• How much does it cost each month?
• How much am I making, and what's my actual profit?
• What renewals are coming up?
• Which costs are growing?

Costwatch is not accounting software. It doesn't do invoicing, taxes, payroll or bank connections, and nothing in it is financial advice. It's a clear, private view of the real operating cost of your software product.

Features

• Multiple products, each with its own currency, with a quick product switcher
• Costs: monthly, quarterly, yearly, custom-interval or one-time, with category, provider, renewal date and notes. Pause a cost or mark it inactive without losing its history.
• Monthly estimate: every recurring cost is converted to a monthly equivalent (clearly labelled as an estimate)
• Revenue: fast manual entry, grouped by month with that month's costs and profit
• Profit and margin, with no divide-by-zero surprises when there's no revenue yet
• Renewals: what charges you in the next 7, 30 or 90 days. Past renewal dates are projected forward and marked as estimated.
• Cost history: price and status changes are recorded automatically, so you can see which costs are growing and how your monthly cost has changed
• Honest currencies: amounts in other currencies are shown separately and never silently converted
• CSV export of costs and revenue, and full account deletion
• Private by default: every row is protected by Postgres Row Level Security
• Responsive, keyboard-accessible, and respects reduced motion

Costs	Renewals	Mobile

Tech stack

• Next.js 16 (App Router, Server Actions), TypeScript, Tailwind CSS 4
• Supabase: PostgreSQL, Auth, Row Level Security
• Hand-rolled SVG charts (no chart library)

No separate backend server: the Next.js app talks to Supabase as the signed-in user.

Repository layout

costwatch/
├── web/                  Next.js application
│   ├── app/              Routes: landing, docs, auth, /app dashboard, server actions
│   ├── components/       UI primitives, charts, forms, app shell
│   ├── lib/              calc.ts (all money math), data/ (server-only data access), validation
│   └── types/            Database types
├── supabase/
│   ├── migrations/       Schema, RLS policies, triggers
│   └── seed.sql          Demo data for local development only
└── docs/                 Architecture, calculations, self-hosting

Local development

Requirements

• Node.js 20.9+ (22 recommended, see .nvmrc)
• Docker, for the Supabase CLI's local stack (or use a hosted Supabase project)

1. Start Supabase

git clone https://github.com/App-Chef/costwatch.git
cd costwatch
npx supabase start       # Postgres, Auth, Studio and a local email inbox
npx supabase db reset    # applies migrations and loads demo seed data

npx supabase status prints the API URL and anon key you need next.

2. Configure the app

cd web
cp .env.example .env.local

Environment variables

Variable	Required	Description
NEXT_PUBLIC_SUPABASE_URL	Yes	Supabase API URL (http://127.0.0.1:54321 locally)
NEXT_PUBLIC_SUPABASE_ANON_KEY	Yes	Supabase anon / publishable key. Safe in the browser because RLS protects all data.
NEXT_PUBLIC_SITE_URL	Production	Public URL, used for auth email links, sitemap and social previews
NEXT_PUBLIC_AUTH_GOOGLE_ENABLED	No	true to show "Continue with Google" (configure the provider in Supabase first)

Costwatch never needs the service_role key. Don't add it.

3. Run the application

npm install
npm run dev

Open http://localhost:3000. Sign in with the demo account demo@example.com / costwatch-demo, or create your own. The demo products ("Amazu" and "Financ") and all their numbers are made-up example data.

Supabase setup (hosted)

1. Create a project at supabase.com.
2. Push the schema:

   npx supabase login
   npx supabase link --project-ref <your-project-ref>
   npx supabase db push

   Or run each file in supabase/migrations/ in order in the SQL editor. Do not load seed.sql into production.
3. In Authentication → URL Configuration, set the Site URL and add https://your-domain.com/auth/callback to the redirect URLs.
4. Configure custom SMTP before inviting real users (Supabase's default sender is heavily rate-limited).
5. Optional: enable the Google provider and set NEXT_PUBLIC_AUTH_GOOGLE_ENABLED=true.

The full guide is in docs/self-hosting.md and at /docs in the app.

Database migrations

Migrations live in supabase/migrations/ and are applied in filename order.

• New changes go in a new migration file. Never edit a released migration.
• Every table with user data must enable RLS, define policies, and set explicit grants.
• After changing the schema, update web/types/database.ts (or regenerate it with npx supabase gen types typescript --local).

Checks

cd web
npm run lint          # ESLint
npm run typecheck     # TypeScript
npm run build         # production build

CI runs all of these on every pull request (.github/workflows/ci.yml).

How the numbers work

• Monthly cost = sum of the monthly equivalents of active recurring costs in the product's currency: yearly ÷ 12, quarterly ÷ 3, custom by interval length.
• Estimated profit = revenue recorded this month − monthly cost.
• Profit margin = profit ÷ revenue × 100, or "No revenue recorded" when revenue is zero.
• One-time costs are listed on their own and aren't part of the monthly cost.

Details and edge cases are in docs/calculations.md.

Contributing

Contributions are welcome. Please read CONTRIBUTING.md and our Code of Conduct first.

Security

Please report vulnerabilities privately. See SECURITY.md.

License

MIT