Expense tracker CLI with CSV import + monthly reports

Resume bullet (when finished)

“Built a SQLite-backed expense tracker with CSV bank-statement import, deterministic category-rules engine, monthly reports as PDF, and 87% pytest coverage.”

Locked tech stack

No "choose your language" — analysis paralysis kills completion. Follow the stack to the letter on your first build.

Milestones (5 · ~13h)

1. M1~2h

   SQLite schema + first migration

   Tables `accounts`, `transactions`, `rules`. Migration via plain SQL files (no ORM).

   CHECK BEFORE MOVING ON:

   • Why SQLite, not Postgres, for this project?
   • Why migrations as plain SQL rather than Alembic?
   $ git commit -m "feat(db): initial SQLite schema + migrations"
2. M2~3h

   CSV import — bank format

   `expenses import statement.csv --account checking` is idempotent (re-running doesn't duplicate). Uses Decimal for amounts.

   CHECK BEFORE MOVING ON:

   • Why never store money as float?
   • How do you make CSV import idempotent without a deduplication ID column?
   $ git commit -m "feat(import): idempotent CSV ingest with Decimal amounts"
3. M3~2h

   Rules-based categorisation

   `rules add 'STARBUCKS' coffee`. On import, every uncategorised row matching the substring gets the category. First match wins, deterministic order.

   CHECK BEFORE MOVING ON:

   • Why deterministic order matters for a categorisation engine.
   • When would you reach for ML instead of rules — and why don't you here?
   $ git commit -m "feat(rules): substring-match categorisation engine"
4. M4~4h

   Monthly PDF report

   `expenses report --month 2026-05 --pdf out.pdf` generates a PDF with totals by category, top-5 expenses, and a sparkline.

   CHECK BEFORE MOVING ON:

   • Why ReportLab instead of WeasyPrint or wkhtmltopdf?
   • What's the right way to test PDF generation without comparing bytes?
   $ git commit -m "feat(report): monthly PDF via ReportLab"
5. M5~2h

   87% test coverage + CI

   pytest + coverage gate at 85% in GitHub Actions. Tests use an in-memory SQLite for speed.

   CHECK BEFORE MOVING ON:

   • Why a coverage *gate* in CI, not just a *report*?
   • What's wrong with chasing 100% coverage?
   $ git commit -m "test: 87% coverage + CI gate"

60-second demo storyboard

What you say in the recruiter screen when they ask "tell me about your latest project." Practice it out loud.

1. 0-5s: 'CLI expense tracker — CSV in, PDF report out, deterministic rules engine.'
2. 5-25s: live demo — import a CSV, add a rule, generate the monthly PDF.
3. 25-45s: show the rules engine code + 'why first-match-wins matters'.
4. 45-60s: pytest --cov; 87% in 1.4s.

STAR talking points for behavioral round

Production references — how grown-up systems do this

Self-review rubric (before you claim done)