Halo Theme Development
Halo is built on Spring Boot + Spring WebFlux + Thymeleaf. Themes use Thymeleaf templates for frontend page rendering.
Important: Halo's APIs, VO field names, and template variables evolve across versions. Do not rely on training data for specific field names, method signatures, or type structures. When writing code that accesses template variables or calls Finder API methods, always fetch the relevant online doc from the References section below first.
Thymeleaf Quick Reference
Core syntax cheatsheet:
<!-- Output text -->
<h1 th:text="${site.title}"></h1>
<!-- Output unescaped HTML -->
<div th:utext="${post.content.content}"></div>
<!-- Links -->
<a th:href="@{${post.status.permalink}}">Post link</a>
<link rel="stylesheet" th:href="@{/assets/dist/style.css}" />
<!-- Loop -->
<li th:each="post : ${posts.items}" th:text="${post.spec.title}"></li>
<!-- Conditionals -->
<div th:if="${posts.hasNext()}">Next page</div>
<div th:unless="${posts.hasNext()}">Last page</div>
<!-- Local variable -->
<div th:with="menu = ${menuFinder.getPrimary()}">...</div>
<!-- Fragment include -->
<div th:replace="~{fragments/header :: header}"></div>
<!-- Layout reuse: pages pass fragments into a parameterized layout -->
<html th:replace="~{layout :: html(head = null, content = ~{::content})}">
<th:block th:fragment="content"><!-- page body --></th:block>
</html>
<!-- Inline JavaScript -->
<script th:inline="javascript">
var url = '[(${#theme.assets("/dist/main.iife.js")})]';
</script>Development Workflow
- Create a theme folder under
themes/in the Halo working directory (must matchmetadata.nameintheme.yaml) - Write
theme.yaml(required) andsettings.yaml(optional) - Create template files under
templates/ - Install and activate the theme in Console → Theme Management
- Visit the frontend to verify
Disable Thymeleaf caching during development: set env var SPRING_THYMELEAF_CACHE=false (Docker), or spring.thymeleaf.cache: false in config (source mode).
Starter Templates
The assets/ directory provides two ready-to-use theme templates:
assets/theme-minimal/— Zero-build-tool minimal theme with all 8 template files; ideal for quick prototyping or simple themesassets/theme-vite/— Vite project template withvite-plugin-halo-theme(recommended for new themes); includes partial layout reuse and CSS toolchain
Usage: copy the directory into themes/ in your Halo working directory, ensure the folder name matches metadata.name in theme.yaml, then install and activate in Console.
References Index
| File | Content | When to read |
|---|---|---|
| references/structure-and-config.md | Directory structure, theme.yaml fields, settings.yaml form definition | Creating a theme, configuring theme.yaml/settings.yaml |
| references/vite-plugin.md | vite-plugin-halo-theme integration guide, include/slot template syntax, TailwindCSS integration | Setting up a Vite-based theme (recommended) |
| references/templates.md | Template route mapping, available variables per template | Writing template files |
| references/global-variables.md | Global variables (site, theme, theme.config) and type definitions | Accessing site info or theme setting values |
| references/finder-apis.md | All Finder APIs (postFinder, categoryFinder, tagFinder, menuFinder, singlePageFinder, etc.) | Querying data from any template |
| references/static-resources.md | Static asset reference methods (@{}, #theme.assets()) | Referencing CSS/JS/images in plain HTML themes |
| references/template-tags.md | Custom tags (halo:comment extension point, halo:footer injection) | Integrating comment plugins, injecting footer code |
| references/official-plugins.md | Official plugin integration: pluginFinder.available(), search widget, dark mode color scheme adaptation | Adding search, adapting dark mode for plugin UI |
| references/annotations.md | AnnotationSetting for model custom fields, #annotations utility for reading metadata in templates | Adding custom fields to menu items/posts/categories and using them in templates |
| references/packaging.md | Packaging a theme as a ZIP using @halo-dev/theme-package-cli | Preparing a theme for release or upload |
| references/thymeleaf-tips.md | Halo-specific Thymeleaf best practices: literal substitutions, safe navigation, meta tag rules, permalink syntax | Writing any template file |