AI can write code faster than any human. But it cannot decide what to build. The engineers who thrive in the AI era are the ones who understand the architectural patterns behind every system. This framework gives you that understanding.
AI tools generate implementation. You provide the architecture. Knowing which building blocks to compose and why is the skill that matters most.
Instagram, Netflix, Uber, Slack, Stripe. Different products, same 7 building blocks. Learn the pattern once, apply it to any system.
The framework is free. Read the articles, try the challenges, use it in your work and interviews. No account required.
Every software system is composed from these 7 universal building blocks. Two handle tasks, five handle storage. Together they can model any system.
Receives a request, does work, sends a response. The backbone of every API.
The call: when the answer has to come back right now.
Picks up tasks from a queue and processes them in the background, at its own pace.
The call: when the work can leave the request and finish on its own.
Lightning-fast lookups by key. Caching, sessions, feature flags.
The call: when a lookup by key has to be instant.
Stores large blobs: images, videos, PDFs. Optimized for size, not queries.
The call: when what you're storing is a whole file, not a record.
Decouples producers from consumers. Makes systems resilient to spikes and failures.
The call: when the work can wait, but must not be lost.
Structured data with relationships. Transactions, constraints, complex queries.
The call: when the data has to stay correct across relationships.
Similarity search for AI. Find content by meaning, not exact match.
The call: when "close enough" is the actual answer you need.
The seven blocks work before you build and after. Two skills put the same framework to work inside Claude Code, one for designing, one for reviewing.
A free, open source skill that designs your application using the seven building blocks: one paragraph in, a labeled architecture and a buildable design doc out, for the moment before you have written a line of code. Built and tested in Claude Code.
A free, open source skill that reviews your system design against the seven building blocks and the non-functional -ilities: what scales, what breaks, and the questions a senior would ask, for the design you already have before you ship it. Built and tested in Claude Code.
The same framework as a free 7-lesson lecture series — the original recordings that started it all. Read the articles, watch the videos, or both.
Seven articles, about an hour and seven minutes end to end, and the framework is yours. Read them in order, or jump to what interests you.
Reading is free. So is the practice: Scaffold runs this same workflow on your own code. Install Scaffold →
You can't read your way to judgment — you have to build. Design Instagram, Netflix, and Uber from the blocks up. Each challenge hands you real requirements and asks you to pick the right blocks and compose them into a working system.
Play the Building Blocks GameYou can name all seven building blocks and the three forces that act on them. That's real ground. Most engineers never get this far. The courses are the guided tour from here: the same knowledge, in order, with the reps that turn it into judgment you can defend under real constraints.
Course I teaches the seven blocks themselves, in 8 video lessons. Courses II through IV apply them to real systems: Content Systems (10 lessons, Instagram, Netflix, YouTube), Real-Time Systems (11 lessons, Slack, Discord, WhatsApp), and Business & Transaction Systems (9 lessons, Stripe, Shopify, Salesforce). Every course pairs 2 labs with a 3-part design challenge and feedback on your design decisions. All four together, one bundle: $299.
Continuing Lecturer at UC Berkeley School of Information. Software engineer and engineering manager with 15+ years building systems at leading technology companies, including AncestryDNA and Morgan Stanley. Teaching engineers to think in systems.
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