The beginner's guide to performance testing
Ninety short parts that take you from "what is load testing" to reading your own reports, written for developers, QA engineers and ecommerce teams who are new to performance work. Each part stands on its own; read in order and the vocabulary builds.
1part published so far. New parts every Wednesday and Thursday; the latest is part 1, .
Foundations
What performance testing is, why speed matters to a business, and what a first load test looks like.
Parts in this module are still to come.
Background reading
- What is load testing?
- Performance testing: the complete guide
- Load testing vs stress testing vs performance testing: how the three actually differ
- Functional testing vs performance testing: two questions every release should answer
- Smoke testing vs performance testing: when a quick pre-release check is enough
How a web page loads
The journey from a typed URL to a rendered page: DNS, TLS, the first byte, caches, scripts and images, and why mobile is slower.
Parts in this module are still to come.
Measuring speed
Core Web Vitals and the metrics around them, the tools that report them, and how to read a score without being misled by it.
Parts in this module are still to come.
Background reading
- Largest Contentful Paint (LCP), explained for engineers
- Interaction to Next Paint (INP), explained for engineers
- How to improve LCP: a step-by-step optimization guide
- How to improve INP: a step-by-step optimization guide
- How to improve CLS: a step-by-step optimization guide
- Core Web Vitals: why lab scores differ from real users
- Core Web Vitals at load, explained
- Why average response time misleads you: reading p95 and p99
- What is an Apdex score? Measuring user satisfaction in performance testing
- 8 metrics every performance test report should include
Load-testing vocabulary
Virtual users, concurrency, throughput, ramp-up and the other words every load test report uses.
Parts in this module are still to come.
Types of tests
Capacity, volume, scalability and the rest of the testing family, and which shape of test answers which question.
Parts in this module are still to come.
Running tests safely
Sizing, duration, environments, test data, pass criteria and the operational blockers every first test hits.
Parts in this module are still to come.
Reading results
Reading a report, spotting results that will not survive production, and explaining the numbers to the people who fund the fix.
Parts in this module are still to come.
Where slowness comes from
Where sites actually slow down under load: databases, caches, third-party services, autoscaling limits and queues.
Parts in this module are still to come.
Ecommerce and peak season
Peak-season readiness for online stores: Black Friday planning, flash sales, checkout and platform-specific slowdowns.
Tools and capstone
Choosing and comparing tools, plus the reference material that ties the guide together.
Parts in this module are still to come.