Rent vs Buy Simulator (Canada-focused)

A Streamlit-based Rent vs Buy financial simulator with a premium dark fintech UI and both deterministic + Monte Carlo analysis.

Disclaimer: This tool is for educational purposes only and is not financial, tax, or legal advice.

Key features

• Deterministic and Monte Carlo evaluation of rent vs buy outcomes
• Before-tax and after-tax reporting
• Breakeven solvers (deterministic + volatility-aware)
• Heatmap exploration with selectable comparison axes
• Scenario save/load with stable st.session_state keys
• Custom dark tooltip system (avoids Streamlit native help popovers)
• Playwright snapshot harness for UI regression safety
• Expert mode hides advanced sensitivity toggles (hypothetical policy + registered shelter approximation)

Expert mode (advanced toggles)

The Taxes & Cash-out panel includes an Expert mode switch. When off (default), the app hides advanced sensitivity knobs like hypothetical capital-gains inclusion changes and the registered-shelter approximation, ensuring baseline behavior stays conservative.

Quick start

1) Install

• Python 3.10+ recommended

pip install -r requirements.txt

For reproducible builds (CI / production):

pip install -r requirements.lock

2) Run

streamlit run app.py

Docker

Build and run with Docker:

docker build -t rbv-simulator .
docker run -p 8501:8501 rbv-simulator

Or use Docker Compose:

docker-compose up

Then open http://localhost:8501.

QA

Run the full QA suite:

python run_all_qa.py

Preflight (recommended before pushing)

Runs repo sanity checks + QA (and optionally visual smoke snapshots).

python scripts/preflight.py
# or
make preflight-fast

To also run Playwright smoke snapshots:

python scripts/preflight.py --run-vr-smoke
# or
make preflight

Visual regression snapshots (UI)

This repo includes a lightweight Playwright harness to prevent "fixed → regressed" UI loops.

Install dev deps:

pip install -r requirements-dev.txt
python -m playwright install --with-deps chromium

Update baselines (writes into tools/visual_regression/baseline/):

python tools/visual_regression/vr_playwright.py --update-baseline

Compare against baselines:

python tools/visual_regression/vr_playwright.py

Smoke snapshots only (no baseline compare):

python tools/visual_regression/vr_playwright.py --smoke

Release process

See docs/RELEASE_CHECKLIST.md for the full checklist (preflight, baselines, tagging, and GitHub release automation).

Project layout

• app.py: Streamlit UI orchestrator
• rbv/: modular core (engine, UI theme, helpers)
• rbv/qa/ + run_all_qa.py: QA gates
• tools/visual_regression/: Playwright snapshot harness
• scripts/preflight.py: repo sanity + QA checks before pushing

Screenshots

Note: Screenshots are captured from the live app. To update, run the Playwright snapshot harness: python tools/visual_regression/vr_playwright.py --smoke

Main Interface

The dark fintech-themed interface with all core inputs visible:

Monte Carlo Analysis

Net worth trajectories with confidence bands from correlated Monte Carlo simulation:

Sensitivity Heatmap

Dual-axis parameter sweep showing buy vs rent outcomes across different scenarios:

Sidebar Settings

Advanced configuration including province selection, mortgage parameters, and economic assumptions:

License

MIT — see LICENSE.