Introduction to Genie.jl

Genie.jl is the core of the Genie Framework with which you can build web apps and backends using Julia. It offers a built-in web server and a flexible system for creating web pages using HTML, JSON, Markdown, or Julia code.

Genie.jl makes your apps fast with built-in caching, keeps user data secure with encrypted cookies and sessions, and helps organize your app with a powerful router for easy navigation. It's a one-stop-shop for developers looking to build efficient and secure web applications with Julia, making the process straightforward and enjoyable.

With Genie.jl you can create pages with dynamic content generated by Julia code. If you'd like to go further and add reactive UIs, check out the Stippe.jl package, which is built on top of Genie.jl.


To install Genie, open a Julia REPL, enter Pkg mode with ] and type

pkg> add Genie

Running Genie interactively at the REPL or in notebooks

The simplest use case is to configure a routing function at the REPL and start the web server. That's all that's needed to run your code on the web page:


julia> using Genie

julia> route("/hello") do
          "Hello World"

julia> up()

The route function defines a mapping between a URL ("/hello") and a Julia function (a handler), which will be automatically invoked to send the response back to the client. In this case we're sending back the string "Hello World".

That's all! We have set up an app, a route, and started the web server. Open your favorite web browser and go to to see the result.


Keep in mind that Julia JIT-compiles. A function is automatically compiled the first time it is invoked. The function, in this case, is our route handler that is responding to the request. This will make the first response slower as it also includes compilation time. But once the function is compiled, for all the subsequent requests, it will be super fast!

Developing a simple Genie script

Genie can also be used in custom scripts, for example when building micro-services with Julia. Let's create a simple "Hello World" micro-service.

Start by creating a new file to host our code -- let's call it geniews.jl

julia> touch("geniews.jl")

Now, open it in the editor:

julia> edit("geniews.jl")

Add the following code:

using Genie, Genie.Renderer, Genie.Renderer.Html, Genie.Renderer.Json

route("/hello.html") do
  html("Hello World")

route("/hello.json") do
  json("Hello World")

route("/hello.txt") do
   respond("Hello World", :text)

up(8001, async = false)

We began by defining 2 routes, and we used the html and json rendering functions (available in the Renderer.Html and the Renderer.Json modules). These functions are responsible for outputting the data using the correct format and document type (with the correct MIME), in our case HTML data for hello.html, and JSON data for hello.json.

The third route serves text responses. As Genie does not provide a specialized text() method for sending text/plain responses, we use the generic respond function, indicating the desired MIME type. In our case :text, corresponding to text/plain. Other available MIME types shortcuts are :xml, :markdown, :javascript and a few others others -- and users can register their own mime types and response types as needed or can pass the full mime type as a string, ie "text/csv".

The up function will launch the web server on port 8001. This time, very important, we instructed it to start the server synchronously (that is, blocking the execution of the script), by passing the async = false argument. This way we make sure that our script stays running. Otherwise, at the end of the script, the Julia process would normally exit, killing our server.

In order to launch the script, run $ julia geniews.jl.

Batteries included

Genie readily makes available a rich set of features - you have already seen the rendering and the routing modules in action. But for instance, logging (to file and console) can also be easily triggered with one line of code, powerful caching can be enabled with a couple more lines, and so on.

The app already handles "404 Page Not Found" and "500 Internal Error" responses. If you try to access a URL that is not handled by the app, like, you'll see Genie's default 404 page. The default error pages can be overwritten with custom ones.