System Design Lens (SDL)¶
System Design Lens (SDL) is a discipline for deliberately designing and evaluating systems.
It treats systems as decision-shaping structures and exists to prevent accidental, vague, or fragile system design.
What SDL is for¶
Use SDL when:
- decisions matter
- systems will be reused or shared
- failures are costly or hard to undo
SDL emphasizes:
- concrete failures over abstract goals
- decisions over activities
- constraints over flexibility
- inspectable artifacts over intentions
- misuse and degradation, not just success
The SDL Book¶
The Discipline of Decision Design book presents the core ideas and reasoning patterns behind SDL.
It is tool-agnostic and focuses on:
- why systems exist
- what decisions they optimize
- how constraints create leverage
- how systems fail when misused
SDL GPT¶
SDL GPT is an AI tool that helps apply System Design Lens in practice.
It enforces SDL discipline by:
- challenging vague system ideas
- requiring concrete failures and decisions
- surfacing assumptions and constraints
- making system structure explicit
SDL GPT supports the discipline; it does not replace it.
Design systems deliberately, not accidentally.