skills/infrastructure/optimize-performance/SKILL.md
Use when optimizing Rails performance — follows a strict workflow: measure baseline, identify bottleneck, write failing RED regression spec asserting query count with db-query-matchers, apply fix, verify spec GREEN, check with EXPLAIN ANALYZE in rails dbconsole, and report quantified improvements. Regression spec must be written before any optimization is applied. Trigger words: performance, optimize, N+1, slow query, caching, Bullet, profiling.
npx skillsauth add igmarin/rails-agent-skills optimize-performanceInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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Identify and fix performance bottlenecks in Rails applications.
| Tool | Use |
|------|-----|
| bullet | N+1 detection in development |
| rack-mini-profiler | Endpoint timing breakdown |
| EXPLAIN ANALYZE | Query plan analysis |
NEVER optimize without a baseline measurement
ALWAYS write a regression spec before optimizing (query count assertion)
ALWAYS verify with EXPLAIN ANALYZE for database changes
NEVER write the report as "I applied includes(:author), then wrote a spec
to lock it in." The spec MUST be written and shown failing BEFORE the fix
appears in your output. Reordering for narrative flow fails the audit even
when the underlying work was correct.
When completing a performance optimization, output MUST follow this seven-step report order. Each step must appear in output:
# Performance Optimization — [Description]
## 1. Baseline
<N> queries for <endpoint/action> — source: <log line / profiler output>
## 2. Bottleneck
<N+1 on association X / missing index on column Y> — tool: <bullet / rack-mini-profiler / EXPLAIN ANALYZE>
## 3. Regression Spec — RED
`make_database_queries(count: <N>)` at <path>:<line> — failure: expected <M>, got <N>
## 4. Fix
<path>:<line> — <includes(:association) / add_index / cache block>
## 5. Regression Spec — GREEN
Spec passes ✓ (<M> queries)
## 6. EXPLAIN ANALYZE
Before: Seq Scan, actual time=<X>ms → After: Index Scan, actual time=<Y>ms
## 7. Quantified Improvement
Queries: <N> → <M> | p95: <X>ms → <Y>ms
Language: English unless explicitly requested otherwise.
Less-Obvious Optimization
# Use counter_cache to avoid COUNT queries in loops
# In migration: add_column :users, :posts_count, :integer, default: 0
# In Post model: belongs_to :user, counter_cache: true
user.posts_count # no extra query
Regression Spec (Query Count Assertion)
RSpec.describe "Post index performance" do
it "loads posts with authors in a fixed number of queries" do
create_list(:post, 10, :with_author)
expect do
get posts_path
end.to make_database_queries(count: 2) # 1 posts query + 1 authors query
end
end
Use the db-query-matchers gem or a custom make_database_queries matcher.
Run directly in rails dbconsole (PostgreSQL) after applying an index or query change:
EXPLAIN ANALYZE
SELECT posts.*, users.name
FROM posts
INNER JOIN users ON users.id = posts.author_id
WHERE posts.published = true;
Reference Files and External Links
Load these files only when their specific content is needed:
External references:
| Skill | When to chain | |-------|---------------| | write-tests | For regression specs | | review-migration | When adding an index |
development
Entry point for Rails development workflows covering TDD, RSpec, Service Objects, DDD, GraphQL, Engines, and Code Quality. Use when the user asks about Ruby on Rails development patterns, needs RSpec test suites generated, wants service objects scaffolded, is setting up GraphQL schemas, performing Rails code review, refactoring .rb files, working with domain-driven design, implementing background jobs, conducting Rails security checks, or building Rails engines. Generates RSpec tests, structures service objects, enforces TDD workflows, configures GraphQL schemas, and coordinates domain-driven design patterns. Trigger keywords: Rails, RSpec, TDD, Rails testing, Rails refactor, Rails API, Rails code review, domain driven design, service objects, GraphQL, Rails engine, Ruby, .rb, background jobs, Rails migrations, Rails security check.
development
Use when shipping a Rails engine gem — FIRST run full test suite (`bundle exec rspec`) and fix ALL failures, verify gemspec metadata and dependencies match tested Rails/Ruby versions, dry-run: `gem build *.gemspec && gem push --dry-run *.gem` and verify contents, generate CHANGELOG.md organized by category (added/changed/deprecated/removed/fixed), produce step-by-step upgrade notes with before/after code, set semantic version in `lib/[engine_name]/version.rb`, document deprecations with migration paths, load release assets conditionally and state which one informed the output. Trigger words: version bump, changelog, deprecation, gemspec, upgrade, release, publish gem, ship gem.
development
Orchestrates the full Rails TDD cycle with hard gates: test MUST exist, be run, and FAIL for the correct reason (e.g. undefined method, not syntax error) before any implementation code — propose minimal implementation and wait for user approval → verify test PASSES → run full suite with rubocop, brakeman, rspec all green → produce YARD documentation and self-reviewed PR; phases context/test design→implementation→iterate→finish. Use when practicing test-driven development, red-green-refactor, TDD workflow, writing tests before code, adding tests first, or building a Rails feature where specs must gate implementation.
development
Complete Rails project setup loop with hard gates: verify Ruby version matches .ruby-version, Bundler installed, database connection successful, all env vars loaded, and ALL external CI actions pinned to immutable commit SHAs (never mutable tags like @v4) → configure CI/CD pipeline with linting, testing, and security scanning → validate end-to-end with bundle install, db:create, db:migrate, rspec, and write SETUP_CHECKLIST.md; phases context/onboarding→CI/CD configuration→environment validation. Use when starting a new Rails project, running `rails new`, configuring a Gemfile or .ruby-version, setting up a development environment, or wiring up CI/CD for a Ruby on Rails app. Trigger: setup project, new Rails app, configure CI/CD, dev environment setup, rails new, Gemfile setup, .ruby-version, Ruby on Rails project bootstrap.