Why I built a SvelteKit + FastAPI SaaS Boilerplate (and open-sourced the starter)

Darren Betney — Tue, 07 Apr 2026 18:47:11 +0000

Every SaaS boilerplate on the market is Next.js.

I searched for months. ShipFast, Supastarter, LaunchFast — all Next.js + Supabase or Prisma. Nothing for the SvelteKit + FastAPI stack that I actually build production apps with.

So I built one.

The Stack

Frontend: SvelteKit 5 (runes syntax), Tailwind CSS v4, TypeScript
Backend: FastAPI, SQLAlchemy async, Pydantic v2
Auth: JWT tokens, bcrypt, email verification, password reset
Billing: Stripe subscriptions (3 tiers), customer portal, webhooks
Database: SQLite (dev) / PostgreSQL (production)
Email: SMTP/Brevo with HTML templates
Deploy: Docker multi-stage build, nginx reverse proxy

What's Included

50+ files extracted from two production SaaS apps I run (a construction management platform and an EHCP tracker for parents).

Multi-tenant authentication with role-based access control (user / admin / superadmin)
Stripe subscription billing with checkout sessions, webhooks, and customer portal
Admin dashboard with user management and system stats
Landing page with animated pricing table
Dark theme with 6-level surface hierarchy and configurable accent color
Docker Compose for one-command production deployment

Why SvelteKit + FastAPI?

SvelteKit 5 with runes is genuinely faster to build with than React. $state, $derived, $effect — no useState/useEffect ceremony. The compiled output is smaller and faster.

FastAPI gives you automatic OpenAPI docs, type validation via Pydantic, and async by default. Combined with SQLAlchemy, you get a backend that's both fast to write and fast to run.

Docker ties it together. One docker compose up -d and you have a production-ready app with nginx, SSL, health checks, and security headers.

Free Starter vs Premium

I open-sourced a lite version with JWT auth, dark theme, and Docker deploy:

Free: github.com/Quartalis/sveltekit-fastapi-starter

The premium version adds Stripe billing, admin dashboard, multi-tenancy, email verification, password reset, and RBAC:

Premium: quartalis.co.uk/store/saas-boilerplate

Live Demo

You can see the starter kit running at demo-saas.quartalis.co.uk — try creating an account and logging in.

If you're building SaaS with SvelteKit + FastAPI, I'd love to hear what you'd want in a boilerplate. The premium version is still evolving and I'm adding features based on what developers actually need.

I built 34 free browser-based developer tools — no accounts, no tracking, no ads

Darren Betney — Tue, 31 Mar 2026 17:26:28 +0000

I got tired of using ad-riddled developer tools that send my data to external servers. So I built my own — 34 of them — and made them all free.

Every tool runs 100% client-side in your browser. No data leaves your machine. No accounts. No cookies. No tracking pixels.

The Tools

Code & Data

Tool	What it does
JSON Formatter	Format, validate, minify JSON with syntax highlighting
Regex Tester	Live match highlighting with capture groups
JWT Decoder	Decode tokens, check expiry, view claims
Base64 Encoder	Encode/decode with UTF-8 support
Diff Checker	Side-by-side text comparison
YAML Validator	Validate syntax + convert to JSON
HTML Entity Encoder	Encode/decode HTML entities
SQL Formatter	Format, beautify, minify SQL queries
Markdown Editor	Live preview editor with GitHub-flavoured Markdown

DevOps & Infrastructure

Tool	What it does
Docker Run to Compose	Convert CLI commands to docker-compose.yml
ComfyUI Workflow Validator	Validate node connections, find broken references
LLM VRAM Calculator	Check if your GPU can run Llama/Qwen/Mixtral
Cron Expression Generator	Visual builder with next-run preview
Ollama Modelfile Validator	Validate Ollama Modelfile syntax and parameters
Port Checker	Check if common ports are open on a host
Power Estimator	Estimate PC power consumption from components

Frontend & CSS

Tool	What it does
Tailwind v3 to v4 Converter	Convert config.js to CSS-first @theme syntax
Svelte 4 to 5 Runes Converter	Convert export let to $props(), $: to $derived
CSS Gradient Generator	Visual linear/radial gradient builder
CSS Box Shadow	Multi-layer shadow builder with inset
Flexbox Generator	Visual layout builder
CSS Unit Converter	px to rem/em/pt/vw/vh
Aspect Ratio Calculator	Calculate and convert aspect ratios

AI & Utilities

Tool	What it does
AI Token Counter	Estimate tokens for GPT-4, Claude, LLaMA + API costs
Password Generator	Web Crypto API, strength indicator, bulk generation
Hash Generator	MD5, SHA-1, SHA-256, SHA-512
UUID Generator	v4 UUIDs with bulk generation
URL Encoder	Encode/decode URIs
Word Counter	Words, chars, sentences, reading time
Lorem Ipsum	Paragraphs, sentences, or words
Timestamp Converter	Unix to human-readable with live clock
QR Code Generator	Generate QR codes with custom colours and sizes
Favicon Generator	Generate multi-format favicons from any image
Roast My Stack	Get your tech stack brutally (but helpfully) roasted

Why client-side matters

Most online tools send your data to a server. JSON formatters, regex testers, even password generators — they often make API calls. Your data goes somewhere.

These tools use:

JSON.parse() / JSON.stringify() for JSON
crypto.subtle for hashing
crypto.getRandomValues() for passwords
RegExp for regex testing
Pure math for VRAM calculations

Nothing leaves your browser tab.

The tech

Built with SvelteKit 5 and Tailwind CSS v4. Statically generated — the entire site is pre-rendered HTML/CSS/JS served from nginx. No server-side processing for any tool.

What's next

I'm adding more tools based on what developers actually search for. If there's a tool you use daily that's either ad-infested or sends data to servers, let me know — I'll probably build a client-side version.

All tools: quartalis.co.uk/tools

Built by Quartalis — a UK software engineering studio. We also sell production-tested Docker stacks, n8n workflows, and SvelteKit starter kits if that's your thing.

DEV Community: Darren Betney