A SvelteKit SaaS boilerplate with a Python backend
FastSvelte is a SaaS boilerplate (we say starter kit, same thing): the code every SaaS needs before it can charge a customer, already written, tested, and maintained. The frontend is a SvelteKit single-page app on Svelte 5. The backend is FastAPI, so the server side is Python. Most SvelteKit boilerplates put Node behind the frontend; this one is for teams whose real work, data, AI, or existing services, lives in Python.
What's in it
- Authentication: sessions in Postgres with HTTP-only cookies, Google login, email verification, password reset, roles.
- Stripe billing: subscriptions, customer portal, webhooks that survive retries and duplicates.
- Multi-tenancy: organizations, roles, and invitations for B2B, or single-user B2C mode.
- AI usage billing: a working AI copilot with token metering, per-plan allowances, and credit top-ups.
- A generated TypeScript client: rename a field in Python and the frontend fails to compile until it's fixed.
- Versioned migrations, admin and user dashboards, transactional email, and deployment guides for five platforms.
Boilerplate vs. prompting it from scratch
The honest comparison isn't against other boilerplates. It's against opening your AI editor and building the base yourself. For a prototype, do that; it's free and fast. The gap shows up in the parts that have to be right before strangers pay you money:
| Prompted from scratch | FastSvelte | |
|---|---|---|
| Auth edge cases | Login works; expiry, reset, and revocation are found in production | Handled and tested on day one |
| Stripe webhooks | Happy path works; retries and duplicate events double-charge | Signature-checked and idempotent |
| Tenant isolation | One missed filter shows one customer another's data | Organization scoping in the data layer |
| Schema changes | Regenerate and hope, once real data exists | Versioned migrations, forward and back |
| Time to charging a customer | Weeks of the parts you didn't know existed | A weekend of building your product |
Why the backend is Python
If your product touches data work or AI, the libraries you need are Python libraries. FastAPI gives them a typed, fast HTTP layer, and the generated client keeps the SvelteKit frontend honest about what the API actually returns. How the two halves fit together, CORS, cookies, deployment, is covered in How to use FastAPI with Svelte.
Maintained, not abandoned
Most boilerplates are a snapshot of the year they were written. FastSvelte ships updates continuously (see the changelog), runs on current Svelte 5 and FastAPI, and is a one-time purchase with full source code. No platform lock-in, no subscription, deploy it anywhere.
Ship production-ready SaaS applications with FastAPI + SvelteKit. Complete authentication, payments, multi-tenancy, and admin dashboards - deploy anywhere with zero vendor lock-in.
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