Tallyo — Invoice SaaS

From Idea to Production-Ready SaaS in One Month

Tallyo is a complete invoice and document management system built as a multi-tenant SaaS. From first idea to 8+ customers in production — with full data isolation, authentication, and Swedish data sovereignty.

The Challenge

The invoice solutions market is dominated by large players with complex systems. What was needed was a fast, focused solution that could be operated by a single person but scale to many customers — without compromising security or data integrity.

The Solution

T1K built the entire system using an AI-first methodology: data models and business logic first, interface second. The result was 50,000+ lines of production code with 31+ API endpoints covering the full chain from document ingestion to invoicing.

The multi-tenant architecture ensures that each customer's data is completely isolated, with authentication and permission controls enforced throughout the entire stack.

Results

• 8+ customers in active production
• 50,000+ lines of code at production quality
• 31+ API endpoints covering the complete business flow
• Swedish data sovereignty — all data on owned servers

Tallyo demonstrates that SaaS systems which would normally take a full development team months to build can be delivered by one person with the right AI tools and a methodical approach. The key is to start with the data, not the interface.