C4 diagram makerfrom plain language, free.

C4Container
  title Online banking system
  Person(customer, "Bank Customer", "Has personal accounts")
  System_Boundary(bank, "Online Banking") {
    Container(web, "Web App", "React", "Banking in the browser")
    Container(api, "API", "Java, Spring Boot", "Accounts, payments and statements")
    Container(mobile, "Mobile App", "Swift and Kotlin", "Banking on the phone")
    ContainerDb(db, "Database", "PostgreSQL", "Users, accounts and transactions")
    ContainerQueue(events, "Events", "Kafka", "Payment and login events")
    Container(notifier, "Notifier", "Node.js", "Alerts and statements")
  }
  System_Ext(core, "Core Banking", "Ledgers and balances")
  System_Ext(email, "Email Service", "Sends email")
  Rel(customer, web, "Uses", "HTTPS")
  Rel(customer, mobile, "Uses")
  Rel(web, api, "Calls", "JSON/HTTPS")
  Rel(mobile, api, "Calls", "JSON/HTTPS")
  Rel(api, db, "Reads and writes", "SQL")
  Rel(api, events, "Publishes")
  Rel(events, notifier, "Delivers")
  Rel(api, core, "Balances and payments")
  Rel(notifier, email, "Sends with")
  UpdateLayoutConfig($c4ShapeInRow="3", $c4BoundaryInRow="1")