Swig

Multi-flavor template engine for Node.js and browsers — native Swig syntax (Jinja2/Django-inspired) and Twig syntax via dedicated frontends sharing one IR backend. gina-io/swig started as a maintained continuation of the abandoned paularmstrong/swig (last released 2014) and is now a standalone project. Security and bug fixes ship here.

Part of the Gina ecosystem. This is the built-in template engine for Gina (npm), a Node.js MVC framework with HTTP/2, multi-bundle architecture, and scope-based data isolation.

Swig is a Jinja2/Django-inspired template engine for node.js and browsers. The syntax will feel familiar to Jinja2 and Django users, but Swig is not drop-in compatible with either — porting templates from an existing project requires a handful of changes. See the Migration Guide for the full parity list and workaround patterns.

Coming from Twig? Install @rhinostone/swig-twig instead — a dedicated Twig-syntax frontend with closer parity than working around incompatibilities here.

Workspace packages

| Package | Description | When to use | | --- | --- | --- | | @rhinostone/swig | Native Swig syntax (Jinja2/Django-inspired). Drop-in for @rhinostone/[email protected] consumers. | Upgrading from @rhinostone/[email protected], or starting fresh with Swig syntax. | | @rhinostone/swig-twig | Twig-syntax frontend with closer Twig parity. | Migrating from PHP Twig, or writing new templates in Twig syntax. | | @rhinostone/swig-core | Shared IR, backend, and runtime primitives. | Building a custom flavor frontend. Otherwise pulled in transitively. |

Each frontend pins the matching @rhinostone/swig-core version exactly during the alpha cycle — the IR is not stable across alpha minors. From 2.0.0 stable onward, frontends and the core release in lockstep.

Features

• Available for node.js and major web browsers.
• Express compatible.
• Object-Oriented template inheritance.
• Apply filters and transformations to output in your templates.
• Hardened against prototype-pollution — __proto__ / constructor / prototype blocked at parser, tag-side, and IR-emission layers. CVE-2023-25345 fully patched. 9 regression cases under tests/regressions.test.js.
• Automatically escapes all variable output (HTML by default; configurable per-call).
• Lots of iteration and conditionals supported.
• Robust without the bloat.
• Extendable and customizable — register custom filters, tags, and loaders per-instance.

Benchmarks

benchmarks/render.js measures sync-render throughput across five workload shapes against Nunjucks.

cd benchmarks && npm install && node render.js

In production-typical settings (autoescape on), @rhinostone/swig outperforms Nunjucks on iteration-heavy templates by 2–3.5× and ties on simple control flow. See benchmarks/README.md for the methodology, the full result table, and how to reproduce on your own hardware.

Need Help? Have Questions? Comments?

• File an issue at gina-io/swig/issues.
• Swig v0.x → v1.x migration notes — the original upstream wiki has been deleted; see HISTORY.md entries around v1.0.0 for the individual breaking changes. For porting from Jinja2 or Django into Swig, see the Migration Guide.

Installation

npm install @rhinostone/swig

For Twig syntax:

npm install @rhinostone/swig-twig

Documentation

User-facing documentation lives in the Gina Docusaurus site under the Swig Template Engine section, maintained in gina-io/docs at docs/swig/. The JSDoc blocks in lib/swig.js, lib/filters.js, lib/tags/, and lib/loaders/ remain the canonical source-of-truth for the public API and are mirrored into the Docusaurus pages.

Basic Example

Template code

<h1>{{ pagename|title }}</h1>
<ul>
{% for author in authors %}
    <li{% if loop.first %} class="first"{% endif %}>{{ author }}</li>
{% endfor %}
</ul>

node.js code

var swig  = require('@rhinostone/swig');
var template = swig.compileFile('/absolute/path/to/template.html');
var output = template({
    pagename: 'awesome people',
    authors: ['Paul', 'Jim', 'Jane']
});

Output

<h1>Awesome People</h1>
<ul>
    <li class="first">Paul</li>
    <li>Jim</li>
    <li>Jane</li>
</ul>

For working example see examples/basic.

Migrating from @rhinostone/[email protected]

@rhinostone/[email protected] is drop-in for 1.x consumers — swig.compileFile, swig.renderFile, swig.setFilter, swig.setTag, and the rest of the public API are unchanged. The internal carve into @rhinostone/swig-core is transparent (test gate during the alpha cycle: byte-identical compiled output against the 1.x test suite).

2.0.0 also ships @rhinostone/swig-twig, a sibling Twig-syntax frontend. Switching is opt-in — your existing @rhinostone/swig install keeps working.

Migrating from Jinja2 or Django

Swig is inspired by Jinja2 and Django, not a drop-in replacement. Common pitfalls when porting existing templates:

• No is / is not / not in operators — rewrite {% if x is defined %} as {% if x !== undefined %}, {% if x not in xs %} as {% if not (x in xs) %}.
• Django forloop.counter → Swig loop.index (Swig follows Jinja2 loop-variable naming).
• {{ super() }} / {{ block.super }} → {% parent %} — Swig uses a dedicated tag inside the overriding block.
• Django filter args use a colon (|date:"Y-m-d") — Swig uses parens (|date("Y-m-d")).
• {% with x=1 %} → {% set x = 1 %}, and no block-form {% set %}…{% endset %}.
• No {% from "f" import x %} — use {% import "f" as ns %} + ns.x instead.
• Method calls require parens — Django auto-invokes x.get_absolute_url; Swig needs x.get_absolute_url().
• ~25 Jinja2 filters are absent — default, truncate, tojson, round, int, float, map, select, batch, trim, etc. Register them via swig.setFilter(name, fn).

Full parity tables and workaround patterns: Migration Guide.

How it works

Swig reads template files and translates them into cached JavaScript functions. The pipeline is: parse → emit IR → lower IR to JS source → new Function(...). At render time, the compiled function runs against a context object to produce the output string.

In 2.x, frontend parsers (native Swig syntax in @rhinostone/swig, Twig syntax in @rhinostone/swig-twig) emit a shared intermediate representation. The backend in @rhinostone/swig-core lowers IR to JS. New flavors plug in at the frontend without touching the runtime.

License

MIT. Copyright (c) 2010-2016 Paul Armstrong and contributors, (c) 2026 Rhinostone. See LICENSE for the full text and AUTHORS for the contributor roster.