GDevelop provides network features that enable games to communicate with remote servers, API or websites.

Everything on the internet uses HTTP requests. When you visit a webpage, your browser sends a request to the web page address, and the website server sends a response with the content of the webpage.

Games and applications work similarly to send or get data to a server:

• they send a request to a specific address (also called an endpoint). Optionally, the request can include parameters.
• the server sends back a response. The set of all requests that are handled by a server is sometimes called an API.

In addition to the address and the parameters, HTTP requests can have a “verb” associated as well. Requests to get data or fetch a webpage are usually “GET” requests. Requests to post data are usually “POST” requests.

GDevelop provides the action called “Send a request to a web page”. You can specify the host and the path to the API/web page to be called (for example, if your “endpoint” is https://mygame.com/api/store-score, the host is https://mygame.com and the path is /api/store-score (don't forget the slash /)). You can also specify the content of the request (the parameter that will be received by the server).

When the server sends the response, it is saved in a variable so that you can read what was sent.

• For GET requests, parameters have to be sent in the content in the format of a “query string”: parameter1=value1&parameter2=value2&parameter3=value3…

You can send data from a variable, for example: "score=" + VariableString(Score) + "&playerName=" + VariableString(Name)

• For POST requests, it depends on what is expected by the server, but most of the time the server expects JSON formatted text.

You can either construct it yourself: "{\"score\": " + VariableString(Score) + " }" (note the use of backslash before the quote \", to allow the quote to be used inside a text) or use the expression to convert a variable structure to JSON: ToJSON(VariableWithData) (see more about this below).

JSON is a text format that can be used to describe the structure of data, containing number, strings, objects and arrays. For example, an object containing the score and the name of a player would be: { "name": John, "score": 45 }.

Variables in GDevelop can contain number, strings or be a “structure” containing children which are also variables, containing number, strings or children.

Children can be manipulated using the usual actions related to variables, by entering their name after a dot after the name of the parent variable (for example, if the variable containing the children is called Progress: `Progress.Level`, `Progress.Score`...).

Structures are useful as they can store all the data concerning something, that can then be sent to a server. To do this, you can convert the structure variable to JSON, using the expression called ToJSON. For example:

ToJSON(Progress)

If the Progress variable has a children “Level” with value 4 and “Score” with value 1500, the resulting JSON will be: {"Level": 4, "Score": 1500}.

You can use it as the content of a request sent to the server.

You can go the other way, and convert JSON back to a variable. This is useful when you've received the answer from the server, which is also usually formatted in JSON.

Use the action “Convert JSON to a variable” (or “Convert JSON to global variable”, or “Convert JSON to object variable”). Specify the JSON to be converted (which will be itself stored in a variable) and the variable, where you need to store the resulting structure.