j2fix

Consistent Jinja2 templates. Less manual cleanup.

j2fix is a command-line formatter for Jinja2 templates, designed around the Arista AVD style guide and the rules enforced by Arista Networks' j2lint. It fixes spacing and statement indentation, then runs j2lint to report anything that still needs your attention.

If you use yamllint to check YAML and yamlfix to tidy it, think of j2fix as the formatting companion to j2lint. It is useful for network configuration templates, Ansible projects, and other Jinja templates that follow Arista's style. You do not need Arista devices or the AVD collection to use it.

An independent project. Not affiliated with or endorsed by Arista Networks.

Usage guide · Security policy · Report a bug

See the difference

Before:

{%for interface in interfaces%}
{%if interface.enabled%}
interface {{interface.name}}
 description {{interface.description|default("Managed by automation")}}
{%endif%}
{%endfor%}

After j2fix interfaces.j2:

{% for interface in interfaces %}
{%     if interface.enabled %}
interface {{ interface.name }}
 description {{ interface.description | default("Managed by automation") }}
{%     endif %}
{% endfor %}

Arista-style nesting goes inside the {% … %} delimiters. The indentation of the configuration text itself stays intact in default mode.

Installation

Requires Python 3.10 or newer. Jinja2 and j2lint are installed automatically.

Install with pip

pip install j2fix
j2fix --version

Quick start

Preview the changes, then apply them:

j2fix --diff templates/
j2fix templates/

Check formatting and lint results without editing files:

j2fix --check templates/

You can pass several files or directories. With no path, j2fix searches the current directory. Directory searches include .j2, .jinja, and .jinja2 files by default.

j2fix router.j2 switch.j2 templates/
j2fix --check .
j2fix --extensions j2,jinja,jinja2,html templates/

Useful commands

Exit codes: 0 means success; 1 means lint issues or changes found in check/diff mode; 2 means a processing error or no matching files. Files may already have been changed in write mode even when the command returns an error.

What to expect

• Spacing and statement indentation are fixed automatically.
• Invalid syntax, variable naming, and other unsupported fixes need manual attention.
• j2fix does not render templates or validate the resulting device configuration.
• --unsafe can change rendered whitespace. Preview it with j2fix --unsafe --diff templates/ and run your rendering tests before applying it.

The current source also adds symlink protection, atomic file replacement, and input limits. See file safety and limits.

Configuration

Optional settings go in your project's pyproject.toml:

[tool.j2fix]
extensions = ["j2", "jinja", "jinja2"]
exclude = [".git", ".venv", "venv", "build", "dist"]
unsafe = false
lint = true
tab_size = 4

j2fix searches upward from your current working directory for these settings. exclude replaces the default exclusions. Keep unsafe = false unless you intend to allow whitespace changes.

See the configuration guide for overrides and limits.

Use with pre-commit

Add this to .pre-commit-config.yaml:

repos:
  - repo: https://github.com/AutoRocket/j2fix
    rev: v0.3.0
    hooks:
      - id: j2fix

Then run:

python -m pip install pre-commit
pre-commit install
pre-commit run --all-files

The hook edits files. Add args: [--check] to check without editing. This example uses the released tag, not unreleased changes on main.

Help and development

For bugs, open an issue with a small, sanitized template, expected output, and your j2fix --version. For security concerns, follow the security policy instead.

See the usage guide for rule coverage, the Python API, and development setup.

License

MIT.

Acknowledgments

This project is based on j2lint Arista Networks’ j2lint.