The Eio-native web framework for modern OCaml.

Documentation: hyphatech.github.io/spindle

Features

• RFC-strict: its own HTTP/1.1 engine, every requirement it meets a test: RFC 9112 and 9110 for HTTP, 6455 for WebSockets, 7578 for forms, and RFC 9651's published suite for Structured Fields.
• Eio-native: straight-line handlers on OCaml 5, multicore by design.
• Typed end to end: JSON derived from your types, every input validated.
• Interactive docs: OpenAPI docs via Scalar at /docs, generated from your routes.
• Front end in sync: Zod or Melange schemas, derived from your OCaml types.
• Batteries included: SQLite and Postgres, WebSockets, SSE, sessions, logging, traces and metrics.

Install

opam repo add hypha https://github.com/hyphatech/opam-repository.git
opam install spindle

Add to your bin/dune:

(executable
 (name main)
 (libraries spindle eio_main)
 (preprocess (pps ppx_wiretype)))

A whole project: your first app.

Example

open Spindle.Syntax

type bill = {
  total : float; [@min 0.]
  tip : int; [@min 0] [@max 100]  (** percent *)
  people : int; [@min 1] [@max 50]
}
[@@deriving wiretype]

type share = { each : float } [@@deriving wiretype]

let split b =
  let total = b.total *. float (100 + b.tip) /. 100. in
  Ok { each = total /. float b.people }

let routes =
  [
    Spindle.post
      Spindle.Path.(s "split")
      (Spindle.Returns.json share_json)
      (let+ b = Spindle.json bill_json in
       split b);
  ]

let () =
  Spindle.Log.setup ();
  Eio_main.run @@ fun env ->
  Spindle.serve env (routes @ Spindle.Openapi.routes routes)

$ curl localhost:8080/split --json '{"total": 90, "tip": 10, "people": 3}'
{"each":33}

Open localhost:8080/docs for interactive API docs, with nothing to write: an OpenAPI 3.2 document generated from your routes, served by Scalar. Every route, its schema with the bounds from your types, every error it may answer, and a button to try it.

Contributing

See AGENTS.md.

Licence

MIT, copyright Hypha Technologies Ltd. See LICENSE.