diff --git a/assets/js/__tests__/tagsinput.spec.ts b/assets/js/__tests__/tagsinput.spec.ts
new file mode 100644
index 00000000..e32b2dfc
--- /dev/null
+++ b/assets/js/__tests__/tagsinput.spec.ts
@@ -0,0 +1,188 @@
+import { $, $$, hideEl } from '../utils/dom';
+import { assertNotNull } from '../utils/assert';
+import { TermSuggestion } from '../utils/suggestions';
+import { setupTagsInput, addTag, reloadTagsInput } from '../tagsinput';
+
+const formData = `<form class="tags-form">
+  <div class="js-tag-block fancy-tag-upload">
+    <textarea class="js-taginput js-taginput-plain"></textarea>
+    <div class="js-taginput js-taginput-fancy">
+      <input type="text" class="js-taginput-input" placeholder="add a tag">
+    </div>
+  </div>
+  <button class="js-taginput-show">Fancy Editor</button>
+  <button class="js-taginput-hide hidden">Plain Editor</button>
+  <input type="submit" value="Save Tags">
+</form>`;
+
+describe('Fancy tags input', () => {
+  let form: HTMLFormElement;
+  let tagBlock: HTMLDivElement;
+  let plainInput: HTMLTextAreaElement;
+  let fancyInput: HTMLDivElement;
+  let fancyText: HTMLInputElement;
+  let fancyShowButton: HTMLButtonElement;
+  let plainShowButton: HTMLButtonElement;
+
+  beforeEach(() => {
+    window.booru.fancyTagUpload = true;
+    window.booru.fancyTagEdit = true;
+    document.body.innerHTML = formData;
+
+    form = assertNotNull($<HTMLFormElement>('.tags-form'));
+    tagBlock = assertNotNull($<HTMLDivElement>('.js-tag-block'));
+    plainInput = assertNotNull($<HTMLTextAreaElement>('.js-taginput-plain'));
+    fancyInput = assertNotNull($<HTMLDivElement>('.js-taginput-fancy'));
+    fancyText = assertNotNull($<HTMLInputElement>('.js-taginput-input'));
+    fancyShowButton = assertNotNull($<HTMLButtonElement>('.js-taginput-show'));
+    plainShowButton = assertNotNull($<HTMLButtonElement>('.js-taginput-hide'));
+
+    // prevent these from submitting the form
+    fancyShowButton.addEventListener('click', e => e.preventDefault());
+    plainShowButton.addEventListener('click', e => e.preventDefault());
+  });
+
+  for (let i = 0; i < 4; i++) {
+    const type = (i & 2) === 0 ? 'upload' : 'edit';
+    const name = (i & 2) === 0 ? 'fancyTagUpload' : 'fancyTagEdit';
+    const value = (i & 1) === 0;
+
+    // eslint-disable-next-line no-loop-func
+    it(`should imply ${name}:${value} <-> ${type}:${value} on setup`, () => {
+      window.booru.fancyTagEdit = false;
+      window.booru.fancyTagUpload = false;
+      window.booru[name] = value;
+
+      plainInput.value = 'a, b';
+      tagBlock.classList.remove('fancy-tag-edit', 'fancy-tag-upload');
+      tagBlock.classList.add(`fancy-tag-${type}`);
+      expect($$('span.tag', fancyInput)).toHaveLength(0);
+
+      setupTagsInput(tagBlock);
+      expect($$('span.tag', fancyInput)).toHaveLength(value ? 2 : 0);
+    });
+  }
+
+  it('should move tags from the plain to the fancy editor when the fancy editor is shown', () => {
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+
+    setupTagsInput(tagBlock);
+    plainInput.value = 'a, b';
+    fancyShowButton.click();
+    expect($$('span.tag', fancyInput)).toHaveLength(2);
+  });
+
+  it('should move tags from the plain to the fancy editor on reload event', () => {
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+
+    setupTagsInput(tagBlock);
+    plainInput.value = 'a, b';
+    reloadTagsInput(plainInput);
+    expect($$('span.tag', fancyInput)).toHaveLength(2);
+  });
+
+  it('should respond to addtag events', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, 'a');
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+  });
+
+  it('should not respond to addtag events if the container is hidden', () => {
+    setupTagsInput(tagBlock);
+    hideEl(fancyInput);
+    addTag(plainInput, 'a');
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+  });
+
+  it('should respond to autocomplete events', () => {
+    setupTagsInput(tagBlock);
+    fancyText.dispatchEvent(new CustomEvent<TermSuggestion>('autocomplete', { detail: { value: 'a', label: 'a' } }));
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+  });
+
+  it('should allow removing previously added tags by clicking them', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, 'a');
+    assertNotNull($<HTMLAnchorElement>('span.tag a', fancyInput)).click();
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+  });
+
+  it('should allow removing previously added tags by adding one with a minus sign prepended', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, 'a');
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+    addTag(plainInput, '-a');
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+  });
+
+  it('should disallow adding empty tags', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, '');
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+  });
+
+  it('should disallow adding existing tags', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, 'a');
+    addTag(plainInput, 'a');
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+  });
+
+  it('should submit the form on ctrl+enter', () => {
+    setupTagsInput(tagBlock);
+
+    const ev = new KeyboardEvent('keydown', { keyCode: 13, ctrlKey: true, bubbles: true });
+
+    return new Promise<void>(resolve => {
+      form.addEventListener('submit', e => {
+        e.preventDefault();
+        resolve();
+      });
+
+      fancyText.dispatchEvent(ev);
+      expect(ev.defaultPrevented).toBe(true);
+    });
+  });
+
+  it('does nothing when backspacing on empty input and there are no tags', () => {
+    setupTagsInput(tagBlock);
+
+    const ev = new KeyboardEvent('keydown', { keyCode: 8, bubbles: true });
+    fancyText.dispatchEvent(ev);
+
+    expect($$('span.tag', fancyInput)).toHaveLength(0);
+  });
+
+  it('erases the last added tag when backspacing on empty input', () => {
+    setupTagsInput(tagBlock);
+    addTag(plainInput, 'a');
+    addTag(plainInput, 'b');
+
+    const ev = new KeyboardEvent('keydown', { keyCode: 8, bubbles: true });
+    fancyText.dispatchEvent(ev);
+
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+  });
+
+  it('adds new tag when comma is pressed', () => {
+    setupTagsInput(tagBlock);
+
+    const ev = new KeyboardEvent('keydown', { keyCode: 188, bubbles: true });
+    fancyText.value = 'a';
+    fancyText.dispatchEvent(ev);
+
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+    expect(fancyText.value).toBe('');
+  });
+
+  it('adds new tag when enter is pressed', () => {
+    setupTagsInput(tagBlock);
+
+    const ev = new KeyboardEvent('keydown', { keyCode: 13, bubbles: true });
+    fancyText.value = 'a';
+    fancyText.dispatchEvent(ev);
+
+    expect($$('span.tag', fancyInput)).toHaveLength(1);
+    expect(fancyText.value).toBe('');
+  });
+});
diff --git a/assets/js/tagsinput.js b/assets/js/tagsinput.ts
similarity index 63%
rename from assets/js/tagsinput.js
rename to assets/js/tagsinput.ts
index bc05b3d7..377db60d 100644
--- a/assets/js/tagsinput.js
+++ b/assets/js/tagsinput.ts
@@ -2,14 +2,20 @@
  * Fancy tag editor.
  */
 
+import { assertNotNull, assertType } from './utils/assert';
 import { $, $$, clearEl, removeEl, showEl, hideEl, escapeCss, escapeHtml } from './utils/dom';
+import { TermSuggestion } from './utils/suggestions';
 
-function setupTagsInput(tagBlock) {
-  const [textarea, container] = $$('.js-taginput', tagBlock);
-  const setup = $('.js-tag-block ~ button', tagBlock.parentNode);
-  const inputField = $('input', container);
+export function setupTagsInput(tagBlock: HTMLDivElement) {
+  const form = assertNotNull(tagBlock.closest('form'));
+  const textarea = assertNotNull($<HTMLTextAreaElement>('.js-taginput-plain', tagBlock));
+  const container = assertNotNull($<HTMLDivElement>('.js-taginput-fancy'));
+  const parentField = assertNotNull(tagBlock.parentElement);
+  const setup = assertNotNull($<HTMLButtonElement>('.js-tag-block ~ button', parentField));
+  const inputField = assertNotNull($<HTMLInputElement>('input', container));
+  const submitButton = assertNotNull($<HTMLInputElement | HTMLButtonElement>('[type="submit"]', form));
 
-  let tags = [];
+  let tags: string[] = [];
 
   // Load in the current tag set from the textarea
   setup.addEventListener('click', importTags);
@@ -27,7 +33,7 @@ function setupTagsInput(tagBlock) {
   inputField.addEventListener('keydown', handleKeyEvent);
 
   // Respond to autocomplete form clicks
-  inputField.addEventListener('autocomplete', handleAutocomplete);
+  inputField.addEventListener('autocomplete', handleAutocomplete as EventListener);
 
   // Respond to Ctrl+Enter shortcut
   tagBlock.addEventListener('keydown', handleCtrlEnter);
@@ -35,19 +41,19 @@ function setupTagsInput(tagBlock) {
   // TODO: Cleanup this bug fix
   // Switch to fancy tagging if user settings want it
   if (fancyEditorRequested(tagBlock)) {
-    showEl($$('.js-taginput-fancy'));
-    showEl($$('.js-taginput-hide'));
-    hideEl($$('.js-taginput-plain'));
-    hideEl($$('.js-taginput-show'));
+    showEl($$<HTMLElement>('.js-taginput-fancy'));
+    showEl($$<HTMLElement>('.js-taginput-hide'));
+    hideEl($$<HTMLElement>('.js-taginput-plain'));
+    hideEl($$<HTMLElement>('.js-taginput-show'));
     importTags();
   }
 
-  function handleAutocomplete(event) {
+  function handleAutocomplete(event: CustomEvent<TermSuggestion>) {
     insertTag(event.detail.value);
     inputField.focus();
   }
 
-  function handleAddTag(event) {
+  function handleAddTag(event: AddtagEvent) {
     // Ignore if not in tag edit mode
     if (container.classList.contains('hidden')) return;
 
@@ -55,14 +61,16 @@ function setupTagsInput(tagBlock) {
     event.stopPropagation();
   }
 
-  function handleTagClear(event) {
-    if (event.target.dataset.tagName) {
+  function handleTagClear(event: Event) {
+    const target = assertType(event.target, HTMLElement);
+
+    if (target.dataset.tagName) {
       event.preventDefault();
-      removeTag(event.target.dataset.tagName, event.target.parentNode);
+      removeTag(target.dataset.tagName, assertNotNull(target.parentElement));
     }
   }
 
-  function handleKeyEvent(event) {
+  function handleKeyEvent(event: KeyboardEvent) {
     const { keyCode, ctrlKey, shiftKey } = event;
 
     // allow form submission with ctrl+enter if no text was typed
@@ -73,7 +81,7 @@ function setupTagsInput(tagBlock) {
     // backspace on a blank input field
     if (keyCode === 8 && inputField.value === '') {
       event.preventDefault();
-      const erased = $('.tag:last-of-type', container);
+      const erased = $<HTMLElement>('.tag:last-of-type', container);
 
       if (erased) removeTag(tags[tags.length - 1], erased);
     }
@@ -86,14 +94,14 @@ function setupTagsInput(tagBlock) {
     }
   }
 
-  function handleCtrlEnter(event) {
+  function handleCtrlEnter(event: KeyboardEvent) {
     const { keyCode, ctrlKey } = event;
     if (keyCode !== 13 || !ctrlKey) return;
 
-    $('[type="submit"]', tagBlock.closest('form')).click();
+    submitButton.click();
   }
 
-  function insertTag(name) {
+  function insertTag(name: string) {
     name = name.trim(); // eslint-disable-line no-param-reassign
 
     // Add if not degenerate or already present
@@ -102,9 +110,9 @@ function setupTagsInput(tagBlock) {
     // Remove instead if the tag name starts with a minus
     if (name[0] === '-') {
       name = name.slice(1); // eslint-disable-line no-param-reassign
-      const tagLink = $(`[data-tag-name="${escapeCss(name)}"]`, container);
+      const tagLink = assertNotNull($(`[data-tag-name="${escapeCss(name)}"]`, container));
 
-      return removeTag(name, tagLink.parentNode);
+      return removeTag(name, assertNotNull(tagLink.parentElement));
     }
 
     tags.push(name);
@@ -116,7 +124,7 @@ function setupTagsInput(tagBlock) {
     inputField.value = '';
   }
 
-  function removeTag(name, element) {
+  function removeTag(name: string, element: HTMLElement) {
     removeEl(element);
 
     // Remove the tag from the list
@@ -134,7 +142,7 @@ function setupTagsInput(tagBlock) {
   }
 }
 
-function fancyEditorRequested(tagBlock) {
+function fancyEditorRequested(tagBlock: HTMLDivElement) {
   // Check whether the user made the fancy editor the default for each type of tag block.
   return (
     (window.booru.fancyTagUpload && tagBlock.classList.contains('fancy-tag-upload')) ||
@@ -142,19 +150,17 @@ function fancyEditorRequested(tagBlock) {
   );
 }
 
-function setupTagListener() {
+export function setupTagListener() {
   document.addEventListener('addtag', event => {
     if (event.target.value) event.target.value += ', ';
     event.target.value += event.detail.name;
   });
 }
 
-function addTag(textarea, name) {
+export function addTag(textarea: HTMLInputElement | HTMLTextAreaElement, name: string) {
   textarea.dispatchEvent(new CustomEvent('addtag', { detail: { name }, bubbles: true }));
 }
 
-function reloadTagsInput(textarea) {
+export function reloadTagsInput(textarea: HTMLInputElement | HTMLTextAreaElement) {
   textarea.dispatchEvent(new CustomEvent('reload'));
 }
-
-export { setupTagsInput, setupTagListener, addTag, reloadTagsInput };
diff --git a/assets/test/vitest-setup.ts b/assets/test/vitest-setup.ts
index 7c0d2d62..ac349f86 100644
--- a/assets/test/vitest-setup.ts
+++ b/assets/test/vitest-setup.ts
@@ -7,6 +7,8 @@ import { fireEvent } from '@testing-library/dom';
 window.booru = {
   timeAgo: () => {},
   csrfToken: 'mockCsrfToken',
+  fancyTagEdit: true,
+  fancyTagUpload: true,
   hiddenTag: '/mock-tagblocked.svg',
   hiddenTagList: [],
   hideStaffTools: 'true',
diff --git a/assets/types/booru-object.d.ts b/assets/types/booru-object.d.ts
index 4154385c..8b04cced 100644
--- a/assets/types/booru-object.d.ts
+++ b/assets/types/booru-object.d.ts
@@ -73,6 +73,14 @@ interface BooruObject {
    * List of image IDs in the current gallery.
    */
   galleryImages?: number[];
+  /**
+   * Fancy tag setting for uploading images.
+   */
+  fancyTagUpload: boolean;
+  /**
+   * Fancy tag setting for editing images.
+   */
+  fancyTagEdit: boolean;
 }
 
 declare global {
diff --git a/assets/types/tags.ts b/assets/types/tags.ts
new file mode 100644
index 00000000..b132dbf0
--- /dev/null
+++ b/assets/types/tags.ts
@@ -0,0 +1,20 @@
+export {};
+
+declare global {
+  interface Addtag {
+    name: string;
+  }
+
+  interface AddtagEvent extends CustomEvent<Addtag> {
+    target: HTMLInputElement | HTMLTextAreaElement;
+  }
+
+  interface ReloadEvent extends CustomEvent {
+    target: HTMLInputElement | HTMLTextAreaElement;
+  }
+
+  interface GlobalEventHandlersEventMap {
+    addtag: AddtagEvent;
+    reload: ReloadEvent;
+  }
+}