Ask Claude to Generate Mermaid Diagrams That Visualize Your Code's Architecture

Sometimes you need to see how your code fits together — for documentation, onboarding, or just understanding a complex flow. Claude can read your actual codebase and generate Mermaid diagrams that render anywhere markdown is supported.

> read the auth system and generate a sequence diagram showing the login flow

Claude traces through your controllers, middleware, services, and models, then outputs something like:

sequenceDiagram
    User->>LoginController: POST /login
    LoginController->>AuthService: attempt(credentials)
    AuthService->>UserRepository: findByEmail(email)
    UserRepository->>Database: SELECT * FROM users
    Database-->>UserRepository: User record
    AuthService->>AuthService: verifyPassword()
    AuthService-->>LoginController: AuthResult
    LoginController-->>User: Redirect + session

You can ask for different diagram types depending on what you need to understand:

> draw a class diagram of the models in app/Models and their relationships

> create a flowchart showing how an order moves through statuses

> generate an ER diagram from my migrations

> draw the request lifecycle through middleware, controller, and service layers

Mermaid diagrams render natively in GitHub READMEs, GitLab, Notion, and most documentation tools — so you can paste Claude's output directly into your docs and it just works.

This is especially powerful for:

• Onboarding docs — show new developers how the system works visually
• Architecture reviews — visualize module dependencies before refactoring
• PR descriptions — add a diagram showing how a new feature's components connect
• Database documentation — auto-generate ER diagrams from your actual schema

Ask Claude to update the diagrams whenever the code changes — keeping docs in sync with reality instead of letting them drift.

A picture of your architecture is worth a thousand lines of code — let Claude draw it from the source.

via Claude Code