Spindle

What is Spindle?

Spindle is a web framework designed for modern OCaml. It provides a fast and ergonomic way to build HTTP servers that strictly follow RFC standards for HTTP/1.1, WebSockets, forms, and structured fields. The framework uses Eio for straight-line handlers on OCaml 5, making it multicore by design.

It enforces type safety end to end by deriving JSON formats directly from OCaml types and validating every input. Developers can generate interactive OpenAPI documentation using Scalar automatically from their route definitions. The system also keeps frontend schemas in sync with backend types using Zod or Melange.

Spindle includes built-in support for SQLite and PostgreSQL databases, along with WebSockets, Server-Sent Events, session management, logging, tracing, and metrics. Installation is handled through the OPAM package manager and integrates with Dune for project builds.

Spindle features

• RFC-strict HTTP/1.1 engine covering multiple RFCs
• Eio-native architecture with multicore support on OCaml 5
• End-to-end type safety with automatic JSON derivation
• Automatic OpenAPI documentation generation via Scalar
• Frontend schema synchronization using Zod or Melange
• Built-in SQLite and PostgreSQL database drivers
• Support for WebSockets, SSE, sessions, logging, and metrics

Who uses Spindle and for what

• Building high-performance REST APIs with strict HTTP compliance
• Creating real-time applications using WebSockets and Server-Sent Events
• Generating shared type definitions between OCaml backends and JavaScript frontends
• Setting up lightweight web services backed by SQLite or PostgreSQL
• Deploying multicore web applications that require efficient concurrency

Spindle FAQ

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