Interactive UI¶

The RWA Calculator ships a polished, locally-run web interface for configuring a run, exploring results, and comparing CRR with Basel 3.1 — backed by a REST API that the UI itself consumes. It is a server-rendered FastAPI + Jinja app styled with the same design tokens as this documentation site, so no JavaScript build step is required and it bundles cleanly for local distribution.

Prerequisites¶

uv add rwa-calc      # or: pip install rwa-calc

The UI dependencies (FastAPI, Uvicorn, Jinja, Marimo) ship with the base package — no extra is required.

Starting the UI server¶

rwa-ui

uv run rwa-ui
# or: uv run python -m rwa_calc.ui.app.main

The server starts on http://localhost:8000 and opens your browser at the landing page.

Pages¶

Charts on the results, comparison and reconciliation pages are rendered as inline SVG themed with the documentation palette.

Calculator¶

The calculator (/calculator) runs the full pipeline through a form.

Submitting validates the data path, runs the calculation, and redirects to the results page for that run. Results show total RWA/EAD, exposure count and average risk weight; the RWA/IRB/SA/Slotting split and output-floor impact; charts of RWA and EAD by exposure class and RWA by approach; and a sample of the exposure-level output. Any data-quality issues are listed beneath the results.

Comparison¶

The comparison page (/comparison) runs the portfolio through both frameworks and shows an executive summary, the additive capital-impact waterfall (scaling factor, supporting factor, methodology, output floor), and a per-class breakdown. It takes roughly twice a single-framework run.

Reconciliation¶

The reconciliation page (/reconciliation) reconciles this calculator's output against a legacy calculator's output, component by component, for migration confidence. Enter your data path, edit the TOML mapping (which names the legacy file, the join keys and how each legacy column maps to a canonical component) directly in the form, and run. The result is shown across four drill-down tiers — the headline tie-out and per-component summary, the by-bucket / by-class / by-approach segmentation, the break worklist ranked by materiality, and a per-key forensic table with a bucket filter — plus CSV / Excel downloads of the full per-key detail. See the Reconciliation guide for the mapping grammar and the output reference.

Workbench¶

The polished pages above are read-only. For ad-hoc analysis, the Workbench page launches the Marimo editor (a separate edit server on port 8002) pointed at workspaces/. Marimo notebooks are reactive, reproducible, and git-friendly plain-Python files; new notebooks start from workspaces/templates/starter.py, which wires in the engine API and the shared sidebar.

REST API¶

The same server exposes a JSON API (the library-first contract — embeddable by other tools). Interactive docs are at /docs (OpenAPI).

curl -X POST http://localhost:8000/api/calculate \
  -H 'content-type: application/json' \
  -d '{"data_path": "/path/to/data", "framework": "CRR", "reporting_date": "2025-01-01"}'

The API is also importable without the web server:

from rwa_calc.api import create_api_app  # a FastAPI app exposing the router

Data requirements¶

The UI expects the same directory layout as the Python API:

your_data_directory/
├── counterparty/counterparties.parquet
├── exposures/
│   ├── facilities.parquet
│   └── loans.parquet
├── collateral/collateral.parquet     # optional
├── guarantee/guarantee.parquet       # optional
└── ratings/ratings.parquet           # optional

See Input Schemas for field requirements.

Packaging for local distribution (moonlit)¶

Because the UI is pure-Python and server-rendered (templates, CSS and SVG charts ship as package data — no JS build artifact), it bundles into a single self-contained zipapp with moonlit:

moonlit build -e rwa_calc.ui.app.main:main -o rwa-ui.pyz

Recipients run rwa-ui.pyz with a matching Python; moonlit extracts to a local cache on first run, so the FastAPI static files (including the brand tokens) serve normally. No Node toolchain or internet access is required.

Troubleshooting¶

Port 8000 already in use — run the app on another port:

uv run uvicorn "rwa_calc.ui.app.main:create_app" --factory --port 8080

Data path not found — use an absolute path and confirm the mandatory files (counterparties, facilities, loans) exist in the expected layout.

Calculation errors — check the issues panel on the results page; see Data Validation for field requirements.

Next steps¶

• Configuration Guide
• Calculation Methodology
• Data Model