What Is SaaS Development?

The Definition

SaaS (Software as a Service) is software delivered over the internet to multiple customers from shared infrastructure, typically accessed through a browser and paid for on a subscription basis, rather than installed and licensed per machine. Gmail, Slack, and Stripe's dashboard are all SaaS products.

What Makes It Architecturally Different

• Multi-tenancy — the system serves many customers ("tenants") from one codebase and infrastructure, with each tenant's data properly isolated.
• Subscription billing — recurring payment handling, plan tiers, upgrades/downgrades, and usage-based billing where relevant.
• Self-service onboarding — new customers typically sign up and start using the product without manual setup.
• Continuous deployment — one codebase serving all customers means updates ship to everyone at once, which raises the bar on testing and rollout safety.
• Scalability from day one — the architecture needs to handle growth in customer count, not just data volume for a single user.

Common Mistakes When Building a First SaaS Product

The most common architectural mistake is building a single-customer application first and trying to retrofit multi-tenancy later — data isolation and tenant-awareness are much harder to bolt on after the fact than to design in from the start, even if you only have one customer on day one.

Getting Started

A SaaS product doesn't need every feature multi-tenant systems eventually have on day one — it needs the core architecture (data isolation, auth, billing hooks) to be sound enough that adding customers doesn't require a rebuild.