devops-guide/docs/type-checking.md

Type Checking

Catch type mismatches at analysis time, not at runtime. Especially valuable in large codebases and across refactors.

Tools by Language

Language	Tool	Notes
Python	mypy, pyright	not built-in; add type hints manually
JavaScript/TS	tsc, flow	TypeScript is the dominant choice
Go	built-in	the compiler enforces types
C++	built-in + clang-tidy	compiler + static analysis

Python — mypy

mypy src/

Configure in pyproject.toml:

[tool.mypy]
python_version = "3.12"
strict = true
ignore_missing_imports = true

Start with strict = false and tighten incrementally. Add # type: ignore sparingly — only where third-party stubs are missing.

TypeScript — tsc

tsc --noEmit        # type-check without emitting JS

tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noEmit": true,
    "target": "ES2022"
  }
}

Tips

• Type checking and linting are separate concerns — run both
• In Python, annotate function signatures first; body annotations add less value
• pyright (Pylance) gives faster feedback in VS Code; mypy is CI-standard