---
name: halo-theme-dev
description: >
  Use when creating or modifying a Halo CMS theme, writing Thymeleaf templates,
  configuring theme.yaml or settings.yaml, calling Finder APIs, using
  vite-plugin-halo-theme, defining theme settings forms, referencing static assets,
  implementing halo:comment or halo:footer extension points, defining model
  annotation fields (AnnotationSetting), adding i18n support, or handling error pages.
  Always use this skill when the user mentions themes, templates, Thymeleaf, theme
  configuration, or wants to customize the frontend appearance of a Halo site —
  even if they do not explicitly say "theme."
---

# 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

Full docs: https://raw.githubusercontent.com/thymeleaf/thymeleaf-docs/refs/heads/master/docs/tutorials/3.1/usingthymeleaf.md

Core syntax cheatsheet:

```html
<!-- 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

1. Create a theme folder under `themes/` in the Halo working directory (must match `metadata.name` in `theme.yaml`)
2. Write `theme.yaml` (required) and `settings.yaml` (optional)
3. Create template files under `templates/`
4. Install and activate the theme in Console → Theme Management
5. 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 themes
- **`assets/theme-vite/`** — Vite project template with `vite-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/api-changelog.md](references/api-changelog.md)               | High-impact theme API changes by Halo version, with docs routes                                                  | Before using version-sensitive APIs or raising `spec.requires`                  |
| [references/structure-and-config.md](references/structure-and-config.md) | Directory structure, theme.yaml fields, root screenshot, settings.yaml form definition                           | Creating a theme, configuring theme.yaml/settings.yaml                          |
| [references/vite-plugin.md](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](references/templates.md)                       | Template route mapping, available variables per template                                                         | Writing template files                                                          |
| [references/global-variables.md](references/global-variables.md)         | Global variables (site, theme, theme.config) and type definitions                                                | Accessing site info or theme setting values                                     |
| [references/finder-apis.md](references/finder-apis.md)                   | All Finder APIs (postFinder, categoryFinder, tagFinder, menuFinder, singlePageFinder, etc.)                      | Querying data from any template                                                 |
| [references/static-resources.md](references/static-resources.md)         | Static asset reference methods (`@{}`, `#theme.assets()`)                                                        | Referencing CSS/JS/images in plain HTML themes                                  |
| [references/template-tags.md](references/template-tags.md)               | Custom tags (halo:comment extension point, halo:footer injection)                                                | Integrating comment plugins, injecting footer code                              |
| [references/i18n.md](references/i18n.md)                                 | Internationalization via `.properties` files, `#messages`, `#locale`, frontend i18n injection                    | Adding multi-language support to a theme                                        |
| [references/official-plugins.md](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](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](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](references/thymeleaf-tips.md)             | Halo-specific Thymeleaf best practices: literal substitutions, safe navigation, meta tag rules, permalink syntax | Writing any template file                                                       |
