Lucky Logo

# The Lucky philosophy

Lucky was designed to solve a few core problems that teams often see. Lucky strives to:

  • Catch bugs at compile time, rather than finding them in production.
  • Spend less time writing tests, because the compiler catches many errors for you.
  • Minimize guesswork with conventions for common tasks.
  • Help developers break things into discrete pieces so things are easy to share and maintain as the codebase grows.
  • Minimize boilerplate code so it’s easy to focus on what your app does better than everyone else.

Lucky was designed for developers that love making reliable products. We think you’ll love it.

# How requests are processed

Diagram of how Lucky handles requests
  1. Browser or client makes an HTTP request.
  2. Lucky routes the request to a matching Action.
  1. Action processes the request. For example:
  1. The Action generates a response for the browser or client. For example:
  1. The response is delivered to the browser or client.

# File structure overview

A new Lucky app is a slightly modified version of a Crystal app.

# src folder

The src folder holds most of your application code. This includes actions for handling requests, queries for database access, pages for rendering HTML, and a few other things.

# config folder

Here are all the files for configuring your application. A new app comes with a few configuration files, but you can add more as you see fit.

# db folder

This folder houses all the database migrations for your app.

# tasks folder

You can put custom tasks here that can be run by the lucky command line tool. See lucky -h for a list of the current tasks.

# public folder

Place any files you wish to be public in here. Files placed in here will be publicly accessible from the root path of your app. (e.g. /robots.txt)

For compiled assets, the asset compiler will move the files in to here for you.

# script folder

This folder contains a setup script for bootstrapping your app by default. Place any other bash style scripts or executables you may need for your app in here.

# spec folder

The test files for your application will go in to this folder.

# Procfile and is used when you run lucky dev. By default there is a web and an assets process that are started. You can add more if you need them.

Procfile is often used in production. Companies like Heroku, use it to determine how it should run the app.

# The src folder

It’s standard convention for Crystal applications to place the main business logic in to this folder, so there’s a lot that is going on here.

# actions folder

This is where classes go that handle incoming web requests.

# actions/mixins folder

Action mixins are modules that you can include in actions. Great for authentication, authorization, setting up finders or ensuring certain headers are set.

# components folder

These are shared view components like displaying flash messages, errors, and default layout components like the head tags.

# css folder

Place your styles in here. By default, Lucky uses SASS, but you can configure for any preprocessor.

# emails folder

The classes used by Carbon along with the email templates are placed in here.

# operations folder

Operations for saving database records or interacting with HTTP forms.

# js folder

Your javascript files will go in here.

# models folder

Put anything that models your business. Database objects go here, but you could also put things like service objects.

# pages folder

Pages used for rendering HTML in response to web requests.

# queries folder

This is where your database queries go.

# serializers folder

This is more common with APIs. These are the files that transform your structured data in to some format like json or xml.


This requires all the files and folders that your app needs to run.


This includes your middleware stack. Add your custom HTTP::Handlers to the middleware method array.


Require your third party dependencies (shards) here.


This file requires the app and starts an HTTP server.

# Adding custom files and folders

The structure in Lucky is to create a folder for like objects/modules, etc… You may find yourself adding things like service objects, custom http handlers, mutations, or maybe even other asset files like images for preprocessing. For each of these, just create a new folder in src/ and be sure to add the require in your src/

e.g. Creating a src/handlers/, be sure to add require "./handlers/**" to src/

See a problem? Have an idea for improvement? Edit this page on GitHub