Rails Boot Time Profiling

Profile Rails application boot time using the require-profiler gem. This skill helps identify which require, load, YAML, and HTTP calls dominate startup time, and provides tools to drill deeper into slow files.

Prerequisites

Before profiling, ensure these conditions are met:

1. The require-profiler gem is in the Gemfile (at minimum in the development group).

2. Eager loading must be enabled for the environment you are profiling. Check the environment config:

# config/environments/development.rb (or the target environment)
config.eager_load = true

If eager_load is false, the profile will miss most application code — only files loaded during boot are captured, and lazy-loaded files will not appear.