{
  "instruction": "Extensions use the init_app pattern, defined in a separate extensions.py file",
  "relevant_when": "Agent configures Flask extensions (CORS, rate limiting, etc.)",
  "context": "Flask extensions must be created as bare instances in app/extensions.py with no app argument. They are bound to the app via ext.init_app(app) inside create_app(). This allows multiple app instances (testing, production) to share extension definitions and avoids circular imports.",
  "sources": [
    {
      "type": "file",
      "filename": "skills/flask-best-practices/SKILL.md",
      "tile": "tessl-labs/flask-best-practices@0.2.0"
    }
  ],
  "checklist": [
    {
      "name": "extensions-in-separate-file",
      "rule": "Extension instances are created in app/extensions.py -- not inline in create_app() or at module level in __init__.py",
      "relevant_when": "Agent sets up Flask extensions"
    },
    {
      "name": "init-app-pattern",
      "rule": "Extensions are created without an app argument (e.g., cors = CORS()) and bound later with ext.init_app(app) inside create_app()",
      "relevant_when": "Agent initializes Flask extensions"
    },
    {
      "name": "no-app-in-constructor",
      "rule": "Extension constructors in extensions.py do NOT receive the Flask app as an argument -- no CORS(app) or Limiter(app)",
      "relevant_when": "Agent creates Flask extension instances"
    }
  ]
}