Jinja2 Template Tester

Jinja2 is the default templating engine for Ansible, Nornir, and SaltStack. Network engineers use it to generate device-specific configurations from a single template and a data source (inventory, IPAM export, YAML vars file). Instead of maintaining one config per device, you maintain one template and a structured data file. This tool lets you test templates interactively before running them against real devices.

This tool supports: variable substitution ({{ var }}, {{ obj.key }}, {{ arr[0] }}), for loops ({% for x in list %}/{% endfor %}), if/elif/else blocks, set statements ({% set x = value %}), comments ({# ... #}), the loop variable (loop.index, loop.first, loop.last, loop.length), and over 40 filters including upper, lower, default, join, replace, sort, length, int, float, tojson, truncate, indent, groupby, and more.

JSON is unambiguous to parse in the browser without a dependency, and is directly compatible with Ansible's variable format when you use 'vars_files' with JSON files or query APIs. If your data is in YAML (Ansible group_vars, host_vars), you can convert it with: python3 -c "import yaml,json,sys; print(json.dumps(yaml.safe_load(sys.stdin.read())))" < your_file.yml

This tool does not support: template inheritance ({% extends %}, {% block %}), {% include %}, custom Jinja2 extensions, the Ansible-specific filters (ipaddr, combine, selectattr with complex tests), macros ({% macro %}), the 'namespace' object for cross-scope variable modification, and Ansible's special variables (inventory_hostname, groups, hostvars). For production Ansible testing, use 'ansible-playbook --check' or the ansible-lint tool.

Inside a {% for %} block, the 'loop' object provides: loop.index (1-based position), loop.index0 (0-based), loop.first (true on first iteration), loop.last (true on last), loop.length (total items), loop.revindex (reverse 1-based), loop.revindex0 (reverse 0-based). Example: {% if not loop.first %}!{% endif %} to add a separator between items but not before the first one.

Yes. The Load Example button shows a realistic Cisco IOS interface configuration template. The same approach works for Juniper (JunOS set commands or JSON-format), Arista EOS (CLI or eAPI JSON), Nokia SR-OS, and any text-based config format. The template syntax is identical to what Ansible and Nornir use, so templates tested here will work directly in your playbooks and scripts.