The Solo Developer's System Design
Like Duolingo, but for The Solo Developer's System Design. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
For the part of you with thirty open tabs that never became anything.
A deep dive: 39 levels across 5 sections, about 78 minutes end to end, roughly 16 days at five minutes a day. It moves through Architecting for Clarity, Data Integrity and Security, Building the Engine, The Production Pipeline, and Scaling and Maintenance. It assumes you already know the basics.
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Key ideas in The Solo Developer's System Design
- UI components should only trigger actions and display state, not manage multi-step workflows
- The Engine contains the 'brain' of the app, independent of the delivery mechanism
- Orchestration layers coordinate between different services like payments and mailers
- Encapsulating rules in an Engine prevents duplicating logic across different entry points
- Mixing business logic into UI components makes them difficult to test and reuse
- API controllers should delegate complex calculations to the Engine
- Separating UI from Orchestration to prevent logic bleed
- The Engine layer's role in encapsulating business rules
- Interfaces allow you to swap a local JSON file for a production Postgres DB easily
- The Engine should depend on abstractions rather than specific database drivers
- Decoupling storage makes the app easier to test using in-memory mocks
- Controllers are responsible for extracting parameters from the HTTP request
- Controllers format the final output into the correct JSON or HTML response
- Controllers should never contain 'if/else' logic regarding business permissions or math
- Treating storage as an implementation detail via interfaces
- The 'Thin Controller' pattern responsibilities
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives The Solo Developer's System Design the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
If you want to calculate a discount, where should that 'brain' logic live to ensure it works for both a website and a mobile app?
Get it right to open this lesson and 38 more in the app.
Where The Solo Developer's System Design takes you
Master the architectural patterns and deployment strategies needed to build, ship, and maintain professional-grade web applications without a team.
- 1
Architecting for Clarity
- The Layered Solo Stack
- Modeling Logic with State Machines
- 2
Data Integrity and Security
- Relational Schema Design for Longevity
- Row-Level Security and Multi-tenancy
- Managing Change with Migrations
- 3
Building the Engine
- API Design for Frontend Autonomy
- Secure Asset Handling with Cloud Storage
- Integrating AI into the Core Logic
- 4
The Production Pipeline
- Containerization with Docker
- The Staging-to-Production Workflow
- Automated Testing and CI Pipelines
- 5
Scaling and Maintenance
- Common Design Patterns for Web Apps
- Observability and Error Handling
5 sections · 13 units · 39 levels. Built to play, not to enroll.
You pick the voice
The Solo Developer's System Design is taught in the The Professor style: clear, structured, thorough. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
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