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Intelligent Accounting SaaS Platform

Intelligent Accounting SaaS Platform

Full-stack SaaS platform for accounting, tax management, and financial intelligence - designed for small businesses.

January 2025 - March 2026
14 months
Founder & CTO - Solo Developer
ACCENSEO
Next.js 16React 19TypeScriptPrisma 7PostgreSQL 16Tailwind CSS 4shadcn/uiBetter AuthVercel AI SDKOpenAIAnthropic ClaudeGoogle GeminiStripeOpen Banking PSD2Teledec EDIDockerVitestPlaywright

Lines of Code

234,292

TypeScript, React, CSS

Features

42

Autonomous modules

API Routes

382

REST endpoints

Database Models

91

Prisma schema models

Presentation

Project definition and scope

The Intelligent Accounting SaaS Platform is a comprehensive, full-stack web application designed for French SMBs and freelancers. It covers the complete spectrum of accounting, tax management, and financial operations that a company must perform to stay legally compliant in France.

Born from a concrète need - managing the accounting of ACCENSEO, a software consulting company.

Domain

Accounting, taxation, financial management, legal obligations for French businesses (PCG, CGI, Code de commerce)

Target Users

SMB directors (B2B), chartered accountants, accounting collaborators - with 6 differentiated roles (Admin, Collaborator, Viewer, Accountant, Accounting, Banking)

Functional Scope
Banking & Open Banking
Invoicing (Sales & Purchases)
Tax Declarations (TVA, IS, CFE...)
Accounting Entries & FEC
AI-Powered Assistant
Bank Reconciliation
Document Management & OCR
Financial Reporting & Forecasts
E-invoicing (DGFIP v3.1)

Objectives, Context, Stakes & Risks

Strategic vision and constraints

Objectives
  • Build a complete accounting platform to autonomously manage ACCENSEO accounting
  • Automate all tax obligations: TVA (CA3), IS, CFE, CVAE, DAS2, PAS - with EDI submission via Teledec
  • Integrate Open Banking for automatic bank transaction synchronization (Nordigen/GoCardless, Bridge, Qonto)
  • Provide an AI layer to assist users with categorization, document analysis, and accounting/tax questions
  • Build a reusable codebase potentially commercializable as a standalone SaaS
Context

The project builds upon a thorough analysis of existing accounting solutions: saved web pages, intercepted API responses (JSON files), extracted JavaScript source code, and systematic screenshots.

A security audit of competing platforms was conducted, identifying several vulnerabilities (IDOR, KYC issues) - this audit informed the secure design of the platform.

A market study of accounting software was conducted, alongside research on Open Banking PSD2 and banking aggregators to choose integration providers. Documentation on electronic invoicing platforms (PDP) was also assembled.

Business Stakes

Accounting Autonomy

Enable ACCENSEO to operate without external accounting provider

Tax Compliance

Meet all filing obligations of a SAS under IS regime, simplified real TVA regime

E-invoicing Ready

Anticipate the French 2026-2027 e-invoicing mandate to avoid any last-minute catch-up

Identified Risks

Regulatory Complexity

French accounting is extremely regulated (PCG, CGI, Code de commerce). Any error in tax calculations can have direct financial consequences.

Maintenance Burden

With 234,000 lines of code and 91 database models, the project reaches a considerable size for a solo developer. Long-term maintenance requires rigorous architecture.

Regulatory Obsolescence

Tax rules change regularly (TVA rates, IS thresholds, e-invoicing planned for 2026-2027). The platform must be designed for easy adaptation.

The Steps - What I Did

Chronological phases and personal contributions

Phase 1
Ideation & Market Research
Early 2025
  • I formalized the initiative and validated the internal business need
  • On the competitive front, I mapped the feature set of existing SaaS accounting solutions
  • I defined the target feature set adapted to a small business (SAS under IS regime)
  • On the regulatory side, I researched Open Banking PSD2, EDI tax filing and e-invoicing regulations
Phase 2
Architecture & Technical Setup
Q1 2025
  • I set up the frontend stack: Next.js 16 + TypeScript + Tailwind CSS 4 + 25 shadcn/ui components
  • On the data side, I provisioned Docker Compose (PostgreSQL 16) and Prisma ORM (91 models)
  • I chose a Feature-Driven architecture structured around 42 autonomous modules
Phase 3
Core Feature Development
Q2 2025 - Q4 2025
  • On authentication, I implemented Better Auth with MFA (email, TOTP, SMS) and accountant login tokens
  • On the banking side, I integrated 3 providers (Nordigen/GoCardless via PSD2, Bridge, Qonto)
  • For invoicing, I built sales invoices, quotes and purchase invoices, each with full status workflows
  • On accounting, I developed the chart of accounts, journals, entries, general ledger, trial balance and FEC
  • I automated the tax declarations (TVA CA3, IS, CFE, CVAE, DAS2, PAS) with EDI submission via Teledec
  • As a complement, I coded a Chrome extension for automated tax form filling on impots.gouv.fr
Phase 4
Advanced Features
Q1 2026
  • I integrated a multi-provider AI assistant (OpenAI, Claude, Gemini) with contextual help
  • On reporting, I delivered the dashboard, balance sheet, P&L, SIG, budget and cash flow forecasts
  • On the legal side, I built general assemblies, registers and statutory auditor workflows
  • For payroll, I implemented payslips, DSN, withholding tax and social contributions
  • In parallel, I designed a dedicated Node.js microservice for automated invoice retrieval

Actors & Interactions

How I collaborated with my AI partner and the external stakeholders

Why my human role was critical

I ran this project as a human + AI duo. As the human developer, I direct the AI through detailed prompts to have it generate production-grade code for a complex accounting platform.

An accounting platform handles regulated financial data - tax calculations, bank reconciliations, legal declarations. The AI generates code fast, but it cannot understand French tax law (CGI, PCG), validate accounting accuracy, or make product decisions about what to build. Every feature required me to bring deep domain expertise to specify it correctly and rigorous verification to avoid financial errors.

My role - Direction & Expertise (~15-20%)
  • I carried the product vision and prioritized features across the accounting and tax scope
  • I brought the accounting/tax domain expertise (PCG, CGI, TVA, IS, CFE, DAS2)
  • For each feature, I wrote the functional specifications and detailed instruction prompts
  • On every generated file, I ran a manual code review - logic, naming, security
  • To validate accounting calculations and tax rules, I wrote dedicated verification scripts
  • After each iteration, I ran systematic regression testing
  • Upfront, I audited the security of competing platforms
  • In parallel, I conducted the Open Banking and e-invoicing regulatory research
Claude Code (AI) - Implementation (~80-85%)
  • TypeScript/React/Next.js code generation across the full stack
  • 42 feature modules with full CRUD and business logic
  • 382 API routes with validation and error handling
  • Prisma schema with 91 models and 63 enums
  • Third-party API integration (Stripe, Open Banking, EDI)
  • UI components with shadcn/ui and responsive layouts
Iterative Development Workflow

Inspired by SDD methodologies: Spec Kit, OpenSpec, BMAD, Kiro (AWS) & Tessl

Results

Impact for myself and for the company

Feature Distribution (42 Features)
Database Model Distribution (91 Models + 63 Enums)
For Me - Skills Acquired & Reinforced Through This Project

Technical Skills

  • I reinforced my mastery of full-stack TypeScript/React/Next.js at production scale
  • On architecture, I pushed the Feature-Driven approach for complex SaaS applications
  • I modeled complex relational data (91 tables, relations, enums)
  • I integrated demanding REST APIs (Open Banking PSD2, Stripe, Teledec EDI)
  • On multi-provider AI, I mastered SSE streaming and structured extraction
  • I developed a Chrome extension (Manifest V3, content scripts)
  • On application security, I audited OWASP, detected IDORs and implemented MFA and RBAC
  • In parallel, I practiced reverse engineering on competitor web applications
  • This project changed the way I work: I now design every feature as a testable, verifiable spec and I reason as an AI-partnered developer rather than a lone coder

Accounting & Tax Domain

  • I mastered the French General Chart of Accounts (PCG)
  • I took ownership of TVA regimes and CA3/CA12 declarations with EDI filing
  • I handled corporate tax (IS - instalments and final payment)
  • I assimilated the economic contributions (CFE, CVAE)
  • On payroll, I took charge of DSN, withholding tax and social contributions
  • I upskilled on electronic invoicing standards (PDP, DGFIP v3.1)
  • On the legal side, I integrated company obligations (AG, registers, annual accounts)
  • I went deep on Open Banking (PSD2, STET), both technical and regulatory
For the Company - Business Impact

5 000 EUR/year

Accounting savings

Traditional accountant fees eliminated (5 000 EUR excl. tax/year, excluding payroll)

10

Tax declaration types

Automated via EDI Teledec

Sage

Payroll outsourced

DSN and payroll managed via Sage Business Cloud Paie, partially automated

42

Autonomous modules

Full coverage of automated accounting operations

Delivered Features Summary:

  • Accounting & Entries: Chart of accounts (general, auxiliary, analytical), journals, entries (sales, purchases, bank), general ledger, trial balance, bank reconciliation, FEC (generation, controls, history), closing entries
  • Banking: Multi-bank connections (Nordigen, Bridge, Qonto), automatic transaction sync, AI-assisted categorization, receipt management, invoice-transaction reconciliation
  • Invoicing: Sales invoices (draft, pending, overdue, collected, cancelled), quotes (draft, sent, accepted, declined, invoiced, expired), purchase invoices, PDF generation, credit notes, e-invoicing
  • Tax: TVA (CA3 monthly/quarterly + simulation), IS (instalments + balance), CFE, CVAE, DAS2, PAS, salary tax, RCM 2777, tax calendar, EDI e-filing via Teledec, Chrome extension for impots.gouv.fr
  • AI: Accounting/tax chat assistant (3 providers), contextual help with detail levels, document analysis with structured extraction (Zod schemas)

Project Aftermath

What happened after delivery and current state

Immediate Future: The platform is still under active development as of March 2026. The latest source file modifications date from March 12, 2026 (API collaborator routes). The focus is on stabilizing core features and preparing for production usage.

Medium-Term Trajectory: Several strategic directions are being explored:

  • Production deployment for ACCENSEO's own accounting needs
  • Electronic invoicing readiness for the upcoming French 2026-2027 mandate - comprehensive PDP documentation (DGFIP v3.1 specifications, semantic annexes, feasibility studies) is already prepared
  • Potential SaaS commercialization - the Feature-Driven architecture with 42 autonomous modules was designed from the start to support multi-tenant operation

The Feature-Driven approach ensures new modules can be added independently without impacting existing functionality, and the multi-provider AI strategy protects against vendor lock-in.

Critical Reflection

How I judge this project with hindsight

Strengths

  • Exceptional functional coverage

    With 42 features, 114 pages and 382 API routes, I cover near the entire scope of professional accounting software.

  • Clean, scalable architecture

    On architecture, I pushed a Feature-Driven approach with autonomous, self-contained modules (components, hooks, services, types).

  • Methodical approach

    Before writing a single line of code, I ran a security audit, a market study and a coverage analysis.

Areas for Improvement

  • Commit history to segment better

    I should have grouped my commits by feature with dedicated branches - it would have improved traceability and code review.

  • Test coverage to reinforce

    On the critical modules (tax calculations, accounting entries, declarations), I would have gained from more unit and integration tests.

What I would do differently
  • Regular commits from day one: I would have disciplined my commits to preserve an exploitable history and enable safe rollbacks.
  • Tests from the start (TDD or at minimum tests for tax calculation functions) - I should have tested the most critical business logic as it was written.
  • Automatic API documentation (Swagger/OpenAPI): I would have set it up for the 382 routes to facilitate future developer onboarding and API consumption.
The lasting lessons this project brought me

One motivated developer with the right tools can produce enterprise-grade software

I shipped 234,000 lines of code in ~14 months, alone - a significant accomplishment that showed me how far AI-assisted development can take a solo developer.

Related journey

Professional experience linked to this achievement

ACCENSEO - CTO & Founder

IT consulting and software company providing comprehensive services: custom software development, system integration, cloud infrastructure, database hosting, and technical advisory. Helping SMEs and mid-cap companies transform their IT systems into competitive advantages.

Skills applied

Technical and soft skills applied

Hard Skills

Architecture & Design5/5

Software & System Architecture

Feature-Driven architecture with 42 autonomous modules and 91 database models - 382 REST API routes with multi-role access control (6 profiles) and DGFIP v3.1 e-invoicing readiness

Software Development5/5

Fullstack Development

234K-line SaaS platform: Next.js 16, React 19, TypeScript, 42 features, 382 API routes

DevOps & Cloud4/5

DevOps, Cloud & Production Industrialization

Docker Compose + PostgreSQL 16 + Open Banking PSD2 (Bridge, Qonto, GoCardless)

Data & AI4/5

Data, AI & Machine Learning

91 Prisma models with complex relational schema: chart of accounts, journals, entries, bank reconciliation, FEC

Security4/5

Application Security & Compliance

Competitor security audit (IDOR, KYC) feeding the platform's secure-by-design conception

Image gallery

Project screenshots and visuals

Tax declaration calendar dashboard with upcoming deadlines, late alerts and summary by declaration type
Tax calendar - Declaration deadlines and status tracking
PDF invoice preview modal with Accenseo branded template showing line items, VAT and totals
Invoice preview - PDF generation with custom branding
VAT CA12 annual declaration form with tax breakdown, deductible VAT lines and simplified regime settings
VAT declaration - CA12 annual form with automatic calculations
Invoice PDF template customization panel with 4 style presets and color theme picker
Template editor - Invoice style and color customization
Legal document model library with filtering by legal form type showing decision templates for different company structures
Legal models - Document templates filtered by company type

Need an accounting SaaS designed?

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