InvoicePlane

InvoicePlane is a self‑hosted, open‑source billing platform that empowers developers to deliver end‑to‑end invoicing solutions without relying on SaaS providers. From a technical standpoint, it exposes a clean MVC architecture built on the CodeIgniter 3 framework (PHP 7+), which keeps the codebase lightweight while still providing a full suite of features such as quote management, client CRM, payment tracking, and e‑invoice compliance. The application is database‑agnostic but ships with support for MySQL/MariaDB out of the box, and can be easily swapped to PostgreSQL or SQLite with minimal configuration changes.

Architecture & Technical Stack

• Language & Framework: PHP 7.4+ with CodeIgniter 3, leveraging its HMVC extension for modularity.
• Templating: Server‑side rendering using PHP views; themes are simple CSS/HTML overlays that can be swapped at runtime.
• Database: MySQL/MariaDB (default), with optional PDO adapters for PostgreSQL; migrations are managed via CodeIgniter’s database forge utilities.
• APIs & Extensibility: REST‑like endpoints are available for external integration, though they are not fully documented; developers can hook into the hooks system and use the provided Events to inject custom logic.
• Payment Integration: Stripe, PayPal, and other gateways are integrated via SDKs; the payment module is pluggable, allowing developers to add new providers with minimal effort.

Core Capabilities for Developers

• Modular Hooks: Custom modules can register callbacks on events such as invoice_created or payment_received, enabling automated workflows.
• Template Customization: PDF and email templates are stored as Blade‑style files, allowing full control over layout without touching core code.
• Multi‑Language Support: Language packs are managed via a community portal; developers can add new locales by extending the lang folder.
• CLI Utilities: A command‑line interface can trigger scheduled tasks like email reminders or report generation, useful for integration into CI/CD pipelines.

Deployment & Infrastructure

InvoicePlane is designed to run on any LAMP/LEMP stack. It requires Apache/Nginx with PHP‑FPM, a relational database, and optional mod_rewrite for pretty URLs. The application is Docker‑ready; the official repository ships a docker-compose.yml that provisions PHP, MySQL, and Nginx with sensible defaults. For scalability, the stateless nature of the web tier means horizontal scaling is straightforward—multiple PHP containers can share a shared database and a common volume for uploads. The lightweight footprint (under 10 MB compressed) makes it ideal for edge deployments or low‑resource VPS instances.

Integration & Extensibility

• Plugin System: Developers can create modules that register routes, models, and views. The module loader scans a designated modules directory, making it trivial to add new features without touching core files.
• Webhooks: Outgoing webhooks can be configured for events like invoice creation or payment receipt, allowing real‑time integration with external CRMs or accounting tools.
• Custom Fields: Both clients and invoices support dynamic custom fields, which can be defined via the UI or programmatically through the API, enabling tailored data capture.

Developer Experience

The project hosts a comprehensive Wiki and an active community forum, which serve as primary documentation sources. While the official API docs are sparse, the source code is well‑structured and commented, making reverse engineering straightforward. Issue tracking on GitHub follows a predictable workflow, and contributors are encouraged to submit PRs through the standard fork‑and‑pull model. Licensing under GPLv3 ensures that any modifications remain open source, fostering a collaborative ecosystem.

Use Cases

• Freelance Platforms: Integrate InvoicePlane into a custom freelance marketplace to provide clients with self‑service invoicing.
• SaaS Billing Layer: Wrap the application behind a front‑end SPA to expose a modern UI while keeping the robust back‑end logic.
• Internal Finance Tools: Deploy on a company intranet to replace legacy billing systems, leveraging the open‑source nature for rapid customization.

Advantages Over Alternatives

• Zero Vendor Lock‑In: Full control over code, database, and hosting environment.
• Low Operational Cost: Minimal resource usage allows deployment on budget VPS or cloud instances.
• Extensible Architecture: Hooks, modules, and webhooks provide a developer‑friendly extension model.
• Compliance Ready: Built‑in e‑invoice support for EU standards reduces the need for custom compliance modules.

In summary, InvoicePlane offers a solid, developer‑centric foundation for building or extending billing solutions. Its lightweight PHP stack, modular design, and strong community support make it an attractive choice for teams that value control, flexibility, and rapid iteration.