Concepts
Plain-English answers to the questions every team keeps getting asked.
Four reference libraries with short, scenario-driven explanations. Use them alongside the roadmaps, or as quick lookups before an interview. Each one is filterable and searchable.
Pick a library
All four libraries follow the same shape: short pages, mermaid diagrams, code examples that do something, common mistakes, and a one-line take-home.
System Design Concepts Live
The most common system design questions answered in plain English: caching, load balancers, consistency, queueing, sharding, distributed transactions, plus AWS / GCP / Azure trade-offs.
Data Engineering Concepts Live
The hard parts of data engineering, distilled. SQL, modeling, file formats, batch, streaming, orchestration, quality, observability, cost, plus warehouse and lakehouse trade-offs.
AI Engineering Concepts Live
The patterns that show up in production LLM systems: tokens and cost math, prompting as code, RAG and retrieval, agents and tool use, evaluation, plus the production layer (latency, caching, routing, security, observability).
Energy Concepts Live
A Sweden-first explanation of how the power grid works for software engineers crossing into energy markets. Frequency, balance, ancillary services, day-ahead and intraday markets, retailers, BRPs, regulation.
How to use a concept library
A library is a reference, not a course. Three habits make it more than a wiki.
Search before you scroll
Each library has a search box and section filters at the top. When you have a specific question, search first. The grid is for browsing; the search is for looking things up.
Bookmark the take-home
Every concept ends with a "quick recap" you can copy into your notes. Reading the take-home once a quarter is a cheap way to keep the basics warm before interviews.
Pair with a roadmap
Each library is the reference behind one of the roadmaps. When a stage mentions something unfamiliar, the concept is one click away. Use them together.
New here? Start with the roadmaps for an ordered path. The concept libraries are the reference you hit when you need a quick answer along the way.