Discourse Site Settings

Use this skill before writing or reviewing ordinary Discourse site settings. For upcoming-change feature flags, also use discourse-upcoming-changes. For database migrations that rename or remove settings, use discourse-migration.

Workflow

1. Find nearby examples with rg; avoid reading all of config/site_settings.yml.
2. Put core settings in config/site_settings.yml; put plugin settings in plugins/<plugin>/config/settings.yml.
3. Add an i18n description under en.site_settings.<setting_name> in the matching config/locales/server.en.yml.
4. Set client: true only when frontend code must read the setting through siteSettings.
5. Prefer an area: for admin grouping when the setting belongs on a filtered settings page.
6. Access settings as SiteSetting.setting_name in Ruby and through @service siteSettings in JS.
7. Add a validator when a setting depends on another site setting for correctness.
8. Write focused tests for behavior controlled by the setting, including default behavior.
9. Use Playwright/browser to visit the admin site settings page and verify the setting name and i18n description render correctly.

Naming

• Use a name that describes the behavior, not only the implementation.
• Use the conventional suffix for typed settings:
  • *_groups for group lists.
  • *_categories for type: category_list.
  • *_category for type: category.
• Avoid _ids in public site setting names for category lists even though values are stored as ids.
• For paired settings, prepend the same feature name so admins can recognize the settings as a related group.

Descriptions

• Write descriptions for admins, not developers.
• State the default or safest interpretation when ambiguity is likely.
• Mention privacy/security boundaries that always apply.
• If a setting only matters when another setting has a certain value, say so in the description.
• When referencing another site setting, use the {{setting:setting_name}} token instead of writing the raw setting name or hardcoding the translated label. This lets the admin UI render the referenced setting consistently and avoids copy drifting when labels change.
• Keep option names consistent with enum values and admin labels.

Common Options

• default: choose a safe default for existing sites. For upload settings, use the id of the seeded upload from db/fixtures/010_uploads.rb.
• min, max, regex, and validator: enforce value constraints server-side; descriptions and frontend affordances are not enough.
• mandatory_values: pipe-separated values that must always remain in the setting. Common for group_list settings that must always include admins/moderators.
• disallowed_groups: pipe-separated group ids hidden from group selectors and stripped from API updates. This only applies to group_list settings.
• requires_confirmation: use for risky changes that need an admin confirmation dialog. Valid values are simple, simple_on_enable, and simple_on_disable; add matching client i18n under admin.site_settings.requires_confirmation_messages.<setting_name> when the default copy is not specific enough.
• themeable: true: only for client-side UI settings that themes may override. Prefer simple types such as bool, integer, list, or enum; normal SiteSetting.setting = value writes are not allowed for themeable settings.
• localizable: use for public text/content settings that content localization may translate. Use a hash for metadata such as max_length: and cooked: true when localized markdown should be cooked.
• area: use the filtered admin settings page key when the setting belongs with an existing admin workflow.
• refresh: true: use when clients should reload after the setting changes.

Setting Types

Start with the simplest type that matches the admin's mental model:

• bool: on/off behavior.
• integer / float: numeric values; set min/max where possible.
• enum: one value from a fixed set; use enum: "ClassName" for reusable translated enums.
• list: multiple values from choices; use list_type: compact for selector-style UI and list_type: simple for reorderable item lists.
• group / group_list: one or many groups; use mandatory_values and disallowed_groups where relevant.
• category / category_list: one or many categories through the category picker.
• tag_list, emoji_list, tag_group_list, host_list, email, username, color, icon, upload, uploaded_image_list, and file_size_restriction: use when the name describes the data shape directly.
• json_schema / objects: structured settings. Prefer these only when a scalar/list setting is not enough, and keep tests around schema validation and serialization.

Category Lists

Use a plain type: category_list when the setting means exactly "these categories". Do not add a scope enum just because the setting involves categories. For example, user-default settings such as default_categories_watching should stay as a single category list; admins are selecting the categories to apply, not defining an include/exclude query scope.

default_categories_watching:
  type: category_list
  default: ""
  area: "user_defaults"

Use the two-setting category-scope pattern only when the feature filters a topic/post result set and admins may reasonably need all/public/include/exclude choices or subcategory control.

xyz_category_scope:
  type: enum
  default: "public"
  enum: "CategoryScopeSiteSetting"
  client: false
  area: "feature-name"

xyz_categories:
  type: category_list
  default: ""
  client: false
  area: "feature-name"
  depends_on:
    - xyz_category_scope
  depends_on_values:
    xyz_category_scope:
      - include
      - include_strict
      - exclude
      - exclude_strict
  depends_behavior: "hidden"
  dependent_setting_display: "inline"

Semantics:

• all: all regular topics.
• public: all non-read-restricted regular topics.
• include: use xyz_categories and their subcategories.
• include_strict: use only xyz_categories.
• exclude: start from all regular topics, then remove xyz_categories and their subcategories.
• exclude_strict: start from all regular topics, then remove only xyz_categories.

The CategoryScopeSiteSetting enum provides translated admin labels for these stored values. Pair it with depends_on_values, depends_behavior: "hidden", and dependent_setting_display: "inline" so the category picker appears under the scope setting only when include/exclude modes need it.

Do not make exclude mean "public minus selected categories" unless the product requirement explicitly says that. It is harder to explain and usually surprises admins.

Example from Discourse AI admin dashboard highlights:

ai_admin_dashboard_highlights_category_scope:
  type: enum
  default: "public"
  enum: "CategoryScopeSiteSetting"
  client: false
  area: "ai-features/admin_dashboard"

ai_admin_dashboard_highlights_categories:
  type: category_list
  default: ""
  client: false
  area: "ai-features/admin_dashboard"
  depends_on:
    - ai_admin_dashboard_highlights_category_scope
  depends_on_values:
    ai_admin_dashboard_highlights_category_scope:
      - include
      - include_strict
      - exclude
      - exclude_strict
  depends_behavior: "hidden"
  dependent_setting_display: "inline"

Recommended description shape:

ai_admin_dashboard_highlights_category_scope: "Choose which categories AI highlights can use. Include and exclude options use {{setting:ai_admin_dashboard_highlights_categories}}. Personal messages are always excluded."
ai_admin_dashboard_highlights_categories: "Categories used when the AI highlights category scope is set to <strong>include</strong> or <strong>exclude</strong>."

Implementation notes:

• Use Category.subcategory_ids(category_id) when non-strict modes include descendants.
• Keep IN (:category_ids) / NOT IN (:category_ids) parameterized; parse category-list values to integers before passing them into SQL.
• Handle empty lists explicitly:
  • Empty include means match nothing.
  • Empty exclude means exclude nothing.
• If results are cached, include both the scope and the configured category list in the cache key.
• Test public default, all, include, include strict, exclude, exclude strict, private categories, personal messages if topics are involved, and subcategories.

Enum Settings

• Prefer stable machine values such as include_strict; let descriptions/admin labels explain them.
• Keep enum values short, lowercase, and underscore-separated.
• When changing values before merge, update all tests and cache keys. After merge, treat value changes as migrations/compatibility work.

Dependent Settings

• Add a validator when one setting only works if another setting is enabled, configured, or has a compatible value.
• Keep dependency enforcement server-side; admin descriptions are not enough.
• depends_on without depends_on_values is for boolean parent settings.
• Use depends_on_values when the parent is an enum/string setting and the dependent only applies to specific values.
• Use depends_behavior: "hidden" when the dependent setting should be hidden until applicable.
• Use dependent_setting_display: "inline" when a hidden dependent belongs visually under its parent; save/reset controls are grouped with the parent setting.
• Test both the valid and invalid combinations.

Review Checklist

• Is the default safe for existing sites?
• Is the setting hidden from the client unless JS needs it?
• Does a dependency on another setting need a validator?
• Does the admin description answer the likely "what does this include?" question?
• Is the setting grouped into the right admin area?
• Was the admin settings page checked in the browser so the name and description render correctly?
• Are cache keys or background jobs affected by setting changes?
• Are private categories, personal messages, subcategories, deleted records, and anonymous access handled where relevant?