Expressa

Expressa is a lightweight, data‑driven middleware layer for Express that turns JSON schema definitions into fully functional REST APIs. Rather than imposing a monolithic framework, it plugs directly into an existing Express application, providing an out‑of‑the‑box admin UI and CRUD endpoints for each defined collection. The core idea is to let developers describe their data model once—using standard JSON Schema—and then expose that model through a RESTful interface, with optional authentication and permission layers handled automatically by the admin panel.

• Runtime: Node.js (ES5/ES6) with Express 4.x as the underlying HTTP server.
• Data Persistence: Supports MongoDB, PostgreSQL (via pg), and flat JSON files, enabling version control or simple local storage. The middleware abstracts the driver layer so that collection schemas are agnostic to the underlying database.
• Schema Definition: Uses JSON Schema to describe fields, types, and validation rules. The admin UI allows live editing of these schemas, which are then persisted in the chosen storage backend.
• Admin Interface: A Django‑like CRUD UI rendered on /admin. It serves as both a schema editor and a permission manager, exposing collection‑level REST endpoints at /api.
• Event System: Developers can attach listeners to request/response cycles (e.g., beforeCreate, afterRead) via middleware hooks, enabling custom validation or transformation logic without modifying the core.

• Auto‑Generated CRUD: Every collection gets standard REST endpoints (GET, POST, PUT, DELETE) with query support via MongoDB query syntax.
• Pagination & Sorting: Query parameters page, pageitems, orderby allow fine‑grained control over result sets.
• Permission & Authentication: Built‑in login endpoint (/users/login) and per‑collection permission tables; developers can extend or replace the auth mechanism.
• Schema Reuse: Shared schemas across collections reduce duplication; frontend developers can consume the same JSON Schema to auto‑generate forms.
• Extensibility: Because Expressa is middleware, any other Express router or third‑party middleware can coexist. Developers can wrap existing endpoints with Expressa’s event hooks to add logging, rate limiting, or custom validation.

• Self‑Hosting: Deploy as a standard Node.js service. No containerization required, but Docker images can be built easily due to the minimal dependencies.
• Scalability: Leverages underlying database scalability. For MongoDB, sharding and replica sets are supported; PostgreSQL scales via connection pooling. Stateless Express processes can be load‑balanced behind a reverse proxy (NGINX, HAProxy).
• Configuration: All options (database URL, admin path, API base) are passed to expressa.admin() and expressa.api(). Environment variables or a JSON config file can drive these settings in production.

• Plugin System: While not a formal plugin API, developers can register custom event listeners on collection routes to inject business logic.
• Webhooks: The event system can trigger external HTTP callbacks, enabling integration with CI/CD pipelines or notification services.
• Custom Middleware: Since Expressa is just middleware, any existing Express middleware (JWT auth, CORS, compression) can be layered before or after it without conflict.
• Frontend Consumption: Exposed JSON Schema and REST endpoints allow front‑end frameworks (React, Vue) to generate CRUD UIs automatically via libraries like react-jsonschema-form.

• Minimal Boilerplate: Adding a collection requires only editing the JSON schema via the admin UI—no code changes.
• Documentation: The README provides clear API endpoint patterns and configuration snippets. Additional inline comments in the source aid understanding of hooks.
• Community & Support: The project is hosted on GitHub with continuous integration via CircleCI. Issues and pull requests are actively managed, fostering a responsive development community.
• Licensing: MIT license ensures freedom to modify and redistribute, making it attractive for open‑source or commercial projects.

• No framework lock‑in: Unlike full CMSs (e.g., Keystone, Strapi), Expressa remains middleware, preserving control over routing and middleware order.
• Schema‑first design: Developers can validate data upfront with JSON Schema, reducing runtime errors.
• Extensible event hooks: Custom logic can be added declaratively via listeners, avoiding deep monkey‑patching.
• Lightweight footprint: Minimal dependencies mean faster startup and lower memory usage compared to heavier headless CMS solutions.
• Open licensing: MIT license allows commercial use without royalties, unlike some proprietary CMSs.

Expressa is ideal for developers who need