align-dotenv

Keep local dotenv files aligned with their templates without losing local values.

The template controls structure and known variables. Your local file controls existing values and whether each variable is active or commented out. Unknown local variables are kept by default. Unsupported local syntax causes a safe failure, not data loss.

Install

Packages: npm · PyPI.

align-dotenv is available for both Python and Node.js development workflows. Both distributions expose the same CLI behavior. The npm package is intended as a development-time CLI; a stable JavaScript library API is not currently promised.

Node.js / npm

Node.js 22+ is supported.

npm install --save-dev align-dotenv

Run it directly:

npx align-dotenv
npx align-dotenv --check

Or add project scripts:

{
  "scripts": {
    "env:align": "align-dotenv",
    "env:check": "align-dotenv --check"
  }
}

The Node.js release is tested on Linux/Ubuntu (including WSL) and Windows with Node.js 22 and 24. macOS is not currently part of the tested release matrix, but installation is not blocked.

Python

Python 3.10–3.14 is supported.

uv tool install align-dotenv
# or
pipx install align-dotenv
# or
python -m pip install align-dotenv

Use

Explicit single-file mode

align-dotenv .env --template .env.example
align-dotenv .env --template .env.example --check
align-dotenv .env --template .env.example --unknown keep    # default
align-dotenv .env --template .env.example --unknown remove  # explicitly drop unknown keys
align-dotenv .env --template .env.example --unknown error   # fail, listing key names only

Project mode

Run without a target or template from the project root:

align-dotenv
align-dotenv --check
align-dotenv --unknown keep    # default
align-dotenv --unknown remove
align-dotenv --unknown error

Project mode recursively discovers .env*.example and .env*.template files and removes the suffix to find the corresponding local target. For example:

project/
├── .env                    ← .env.example
├── .env.example
└── apps/api/
    ├── .env.development    ← .env.development.template
    └── .env.development.template

Only existing targets are aligned; templates with missing targets are skipped and reported, never used to create targets. If two templates map to the same target (such as .env.example and .env.template), the command fails without writing.

Discovery is sorted by target path and skips .git, node_modules, .venv, venv, and __pycache__ directories, as well as directory symlinks.

Project mode validates and reconciles every pair in memory before writing any target. An invalid pair or --unknown error failure prevents all writes. After a successful preflight, changed files are replaced atomically one at a time; this is not a cross-file transaction. Unchanged files are not rewritten.

--check performs the same full preflight without writing:

• exit 0: everything is aligned
• exit 1: at least one target needs alignment
• exit 2: invalid invocation, input, or project state

Reconciliation

Given .env.example:

# Required setting
REQUIRED=template

# OPTIONAL=template

and a local .env:

OPTIONAL='local choice'
REQUIRED=local

alignment produces:

# Required setting
REQUIRED=local

OPTIONAL='local choice'

The template keeps control of layout while existing local values and active/commented state are preserved.

Syntax and safety

Understand it, preserve it, or refuse to modify it.

Supported assignments are:

• KEY=value
• export KEY=value
• # KEY=value
• # export KEY=value

Keys must match [A-Za-z_][A-Za-z0-9_]*. Values are preserved as raw text; align-dotenv is intentionally not a full shell or dotenv interpreter.

Unsupported meaningful local content, such as shell directives, line continuations, or unclosed quoted values, stops the operation without modifying the file. Errors report safe metadata such as line numbers or unknown key names, not dotenv values.

The existing target must be a regular file, not a symlink or the template itself. Known lines follow the template's line endings and final newline. Unknown assignments kept by default retain their original representation. Changes are replaced atomically within the target directory, mode bits are preserved where meaningful, and already aligned files are not rewritten.

Development

Run the Python and Node.js suites from the repository root:

PYTHONPATH=src python -m unittest discover -s tests -v
python -m compileall -q src tests

npm --prefix node ci
npm --prefix node test
npm --prefix node run test:package

node scripts/check-versions.mjs

See CONTRIBUTING.md for contributor guidance and node/README.md for Node.js-specific implementation and packaging details and npm CLI usage.