SOLID Review Checklist

Use this reference when running a SOLID review step by step. Each step lists the questions to ask, the signal that a refactor is needed, and the output to record.

Output format

Record each finding in three lines:

<Principle> violation: <what is wrong and where>.
Refactor: <the change>.
Validation: <how to confirm the problem is gone>.

SRP: one reason to change

  • Does the class handle more than one concern, such as business logic, persistence and notifications?
  • Would changes to different features require editing this class?
  • Signal: multiple concerns in one class. Split into focused classes.

OCP: extend without modifying

  • Do new features require editing existing code?
  • Could abstraction or polymorphism remove the edit?
  • Signal: adding a feature edits stable code. Introduce an abstraction and add implementations.
  • Prefer composition and injection over deep inheritance to achieve extension.

LSP: substitutable subtypes

  • Do subtypes strengthen preconditions or weaken postconditions?
  • Do clients need to check types before using a value?
  • Signal: a subtype breaks parent assumptions. Redesign the hierarchy, or return a Result type where the base contract promises no exceptions.

ISP: client-shaped interfaces

  • Do clients depend on methods they never call?
  • Does one interface hold several unrelated method groups?
  • Signal: clients ignore many methods. Split by client role, but keep cohesive method sets together rather than one method per interface.

DIP: depend on abstractions

  • Do high-level modules depend on low-level modules?
  • Are concrete types instantiated inside business logic?
  • Signal: direct concrete coupling. Introduce an interface or port and inject the implementation.

Candidate searches

These searches find candidates only. Inspect each hit before calling it a violation.

rg -n "class.*Service.*Repository|class.*Manager.*Handler" src
rg -n "instanceof|typeof.*==|switch.*type" src
rg -n "new [A-Z].*Repository\(|new [A-Z].*Service\(" src

Judgement

Apply SOLID where the design causes pain: tight coupling, frequent change in one direction, or difficulty testing. Do not extract an interface for every class.

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