--- title: "Intelligent Accounting SaaS Platform" description: "Full-stack SaaS platform for accounting, tax management, and financial intelligence - designed for small businesses." locale: "en" canonical: "https://portfolio.josedacosta.net/en/achievements/plateforme-comptabilite-saas" source: "https://portfolio.josedacosta.net/en/achievements/plateforme-comptabilite-saas.md" html_source: "https://portfolio.josedacosta.net/en/achievements/plateforme-comptabilite-saas" author: "José DA COSTA" date: "2025" type: "achievement" slug: "plateforme-comptabilite-saas" tags: ["Next.js 16", "TypeScript", "Prisma", "PostgreSQL", "Better Auth", "AI SDK", "Open Banking", "Stripe"] generated_at: "2026-06-02T15:38:08.063Z" --- # Intelligent Accounting SaaS Platform Full-stack SaaS platform for accounting, tax management, and financial intelligence - designed for small businesses. **Date:** January 2025 - March 2026 **Duration:** 14 months **Role:** Founder & CTO - Solo Developer **Technologies:** Next.js 16, TypeScript, Prisma, PostgreSQL, Better Auth, AI SDK, Open Banking, Stripe ### Key Metrics - Lines of Code: **-** - TypeScript, React, CSS - Features: **-** - Autonomous modules - API Routes: **-** - REST endpoints - Database Models: **-** - Prisma schema models ## Presentation _Project definition and scope_ ### 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) 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. ### 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_ ### 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. ### 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 ### 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. ### 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 ### Business Stakes ### Identified Risks ## The Steps - What I Did _Chronological phases and personal contributions_ ### Feature Development Over Time ### 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 ### 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 ### 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 ### 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 ### 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 ### External Stakeholders - Teledec - DGFiP-approved EDI partner for tax e-filing - GoCardless (Nordigen) - Open Banking PSD2 provider (2400+ European banks) - Bridge - Banking aggregation provider - Qonto - Neobank with dedicated API - Stripe - Payment platform for SaaS subscriptions - OpenAI / Anthropic / Google - AI providers for the accounting assistant 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. ### Iterative Development Workflow Inspired by SDD methodologies: Spec Kit, OpenSpec, BMAD, Kiro (AWS) & Tessl ## Results _Impact for myself and for the company_ ### 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 - 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 ### Codebase Metrics ### Feature Distribution (42 Features) ### Feature Coverage Analysis ### Database Model Distribution (91 Models + 63 Enums) ### Development Effort Distribution ### For Me - Skills Acquired & Reinforced Through This Project ### For the Company - Business Impact **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. ## Skills applied _Technical and soft skills applied_ - **[Problem Solving & Adaptability](https://portfolio.josedacosta.net/en/skills/problem-solving-adaptability.md)** - PCG, CGI, Code de commerce, EDI Teledec, PSD2 and 2026-2027 e-invoicing preparation, Mastered French accounting domain, Open Banking PSD2, and EDI tax filing from scratch - **[Software & System Architecture](https://portfolio.josedacosta.net/en/skills/system-architecture-design.md)** - 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 - **[Fullstack Development](https://portfolio.josedacosta.net/en/skills/fullstack-development.md)** - 234K-line SaaS platform: Next.js 16, React 19, TypeScript, 42 features, 382 API routes - **[DevOps, Cloud & Production Industrialization](https://portfolio.josedacosta.net/en/skills/devops-cloud-production.md)** - Docker Compose + PostgreSQL 16 + Open Banking PSD2 (Bridge, Qonto, GoCardless) - **[Data, AI & Machine Learning](https://portfolio.josedacosta.net/en/skills/data-ai-machine-learning.md)** - 91 Prisma models with complex relational schema: chart of accounts, journals, entries, bank reconciliation, FEC - **[Application Security & Compliance](https://portfolio.josedacosta.net/en/skills/application-security-compliance.md)** - Competitor security audit (IDOR, KYC) feeding the platform's secure-by-design conception ## 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. ## Image gallery _Project screenshots and visuals_ ## Need an accounting SaaS designed? I delivered this SaaS for accounting firms: automated data entry, consolidated reports and custom validation workflows. Let's talk about your context. **Contact me**