Entry
Sensible entities and responsibilities, basic interfaces and state, and clear communication.
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Learn to turn interview requirements into clear responsibilities, interfaces, state, failure behavior, and a design that can survive follow-up changes.
Low-Level Design focuses on Internal responsibilities, interfaces, and state. System Design covers Distributed architecture; continue there only when that boundary takes over.
Each lesson pairs a concrete example with common mistakes, trade-offs, follow-ups, and a clear stopping point.
Turn an ambiguous object-design prompt into a small, testable model rather than a class inventory.
18 min · Entry / Mid / Senior / Staff+Make scope, actors, success criteria, and non-goals explicit so the model solves a real problem.
16 min · Entry / Mid / Senior / Staff+Choose entities, value-like concepts, and policies from identity, state, and behavior - not every noun in the prompt.
19 min · Entry / Mid / Senior / Staff+Give decisions, mutation, lifecycle, and side effects a clear home so the design stays cohesive as it evolves.
20 min · Entry / Mid / Senior / Staff+Choose collaboration boundaries from the operations that must happen together and the variations you actually need.
19 min · Entry / Mid / Senior / Staff+Protect meaningful transitions and error contracts so a design survives unhappy paths and requirement changes.
22 min · Entry / Mid / Senior / Staff+Treat Strategy, Factory, Observer, State, Adapter, Command, Repository, and composition as options - not a checklist.
21 min · Entry / Mid / Senior / Staff+Identify when simultaneous actions, seams, and requirement changes matter - without turning every design into a distributed system.
24 min · Entry / Mid / Senior / Staff+Choose a lesson when you need a reasoning tool. Choose a practice design when you are ready to explain an approach aloud.
For live-round communication and recovery, use the Playbook execution dossier.
Use this as a rehearsal guide, not a rigid script. Go back to an earlier step when a use case or follow-up reveals a bad assumption.
Confirm the artifact, primary use case, actors, constraints, and what is deliberately out of scope.
Name the one or two flows that should drive the first design before collecting every possible feature.
Keep only concepts with meaningful identity, state, or behavior; nouns alone do not earn a class.
Give each decision, state transition, and side effect one understandable owner.
Choose composition, references, and interfaces from collaboration and lifecycle - not a diagram convention.
State what can change, who may change it, and what must remain true after every operation.
Define validation, error contracts, and edge cases alongside the happy path.
Add a pattern only when a concrete variation, policy, or integration boundary makes it earn its cost.
Trace a representative flow, discuss test seams and concurrency where relevant, then apply one change and explain its trade-off.
Each exercise introduces a different design pressure and keeps its example approach progressively disclosed.
Every level still needs a coherent primary flow and validation. The difference is the judgment expected around ambiguity, evolution, and boundaries.
Sensible entities and responsibilities, basic interfaces and state, and clear communication.
Stronger abstractions, error behavior, extension points, and testability.
Ambiguity, lifecycle, concurrency where it matters, trade-offs, and evolution.
Scope judgment, system and organizational boundaries, and avoiding needless complexity.
LLD stays a secondary public preparation surface in v1. Reaching a lesson’s end records a read marker; practice activity remains separately self-reported. Neither is a mastery or readiness claim.