Rack::SteadyETag generated stable ETags for responses that only changed in CSRF tokens or CSP nonces. Rails apps should be configured to return identical HTML for the same resource and user.

Rails JSON serializes times with milliseconds, so iso8601 and to_json can differ in RSpec expectations. Using to_json keeps time string comparisons matching.

Persist ActiveRecord records directly when callbacks and validations are unnecessary; Rails 2 has create_without_callbacks and update_without_callbacks, while Rails 3 needs sneaky-save.

Serving files as downloads in Ruby on Rails uses send_file; it returns the file directly and overrides the normal render response.

reverse_order breaks on complex SQL sorting and can generate invalid queries in Rails 4; Rails 5 raises ActiveRecord::IrreversibleOrderError instead.

Bundler support for Rails 2.3.x requires updated RubyGems and Passenger, a bundled Gemfile workflow, and bundle exec for tests and deployment.

Database transactions can roll back after after_save, leaving Sidekiq jobs queued for records that never persist. after_commit runs after persistence and avoids this race.

CSS sprites can reduce image requests by bundling small backgrounds into one sprite; Compass and compass-rails automate sprite generation in Rails apps.

Rails secrets and other configuration values can be read inside webpack bundles with rails-erb-loader, enabling environment-specific client-side settings without hardcoding them.

Byebug 11.1.3 can trigger NameError with Rails 6 zeitwerk autoloading; binding.pry, eager loading, or another debugger avoid the issue.

1.year returns a Float in Rails < 4 and can break code that expects an integer duration; Rails 4 uses ActiveSupport::Duration instead.

Rails asset management becomes easier with bower-rails, using a Bowerfile and rake tasks to install, list, update, and rewrite vendored front-end packages.

Rails routing can make singleton collection pages awkward to place under a namespace without adding :project_id; custom controller paths or namespace/resource combinations keep URLs and controllers aligned.

Splitting Rails route definitions across multiple files can improve organization in larger apps. Rails::Engine and config.paths['config/routes.rb'] can load route files from config/routes/.

Create a Time in a fixed timezone regardless of Rails or system settings; useful for tests and API date comparisons when parsing otherwise shifts by environment.

Rails has both truncate helper and String#truncate; the helper is preferred for block support and safer HTML handling, especially with escape: false.

Rails 2 apps can break on MySQL 5.7; MariaDB 10.x is a compatible replacement for old and new applications, with gem rebuilds sometimes needed after switching.

Webpacker-only Rails deploys can fail on deploy:assets:backup_manifest because capistrano-rails expects Sprockets assets. Clearing that task avoids the missing manifest error.

Terminator can split Rails debugging into separate panes, keeping the web server and other Procfile processes visible without mixed log output.

ActionMailer defaults to http in email links, which can expose session cookies to SSL-stripping. Set default_url_options or the link protocol to use https where needed.

ActiveRecord migrations can break when STI models are referenced directly; embedding model classes in the migration and overriding find_sti_class and sti_name keeps type lookup working.

Recent Rails 2 CookieStore versions can emit malformed Set-Cookie headers with blank lines, breaking Cucumber integration tests when cookies are written more than once.

create_with and where can bypass Rails 3 mass-assignment protection, allowing protected attributes to be set from untrusted input.