Screeps has a handy embedded code editor for writing game scripts. However, in some cases (for example, you want to use a language other than JavaScript or integrate with your IDE) you will have to commit game scripts to your Screeps account from outside.

You have to create an auth token in the account settings in order to use external synchronization.

Using Grunt task

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

npm install grunt-screeps

Configure your Gruntfile.js:

module.exports = function(grunt) {

    grunt.loadNpmTasks('grunt-screeps');

    grunt.initConfig({
        screeps: {
            options: {
                email: '<your e-mail>',
                token: '<your auth token>',
                branch: 'default',
                //server: 'season'
            },
            dist: {
                src: ['dist/*.js']
            }
        }
    });
}

Now you can run this command to commit your code from dist folder to your Screeps account:

grunt screeps

Using direct API access

Screeps Web API has an endpoint https://screeps.com/api/user/code for working with scripts. The two supported methods are POST and GET for writing and retrieving respectively. Both methods accept Basic access authentication. Endpoints get and return a JSON structure containing modules object with module names as keys and their content as values.

An example of committing code using Node.js:

var https = require('https');

var email = '<your e-mail>',
    password = '<your password>',
    data = {
        branch: 'default',         
        modules: {
            main: 'require("hello");',
            hello: 'console.log("Hello World!");'
        }
    };

var req = https.request({
    hostname: 'screeps.com',
    port: 443,
    path: '/api/user/code',
    method: 'POST',
    auth: email + ':' + password,
    headers: {
        'Content-Type': 'application/json; charset=utf-8'
    }
});

req.write(JSON.stringify(data));
req.end();

Request:

POST /api/user/code HTTP/1.1
Content-Type: application/json; charset=utf-8
Host: screeps.com:443
Authorization: Basic PHlvdXIgZS1tYWlsPjo8eW91ciBwYXNzd29yZD4=
Connection: close
Transfer-Encoding: chunked

{"branch":"default","modules":{"main":"require(\"hello\");","hello":"console.log(\"Hello World!\");"}}

Response:

X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 8
Date: Mon, 02 Feb 2015 18:46:11 GMT
Connection: close

{"ok":1}