diff --git a/app/data/LocalizationProcessor.test.mjs b/app/data/LocalizationProcessor.test.mjs
new file mode 100644
index 0000000..0236166
--- /dev/null
+++ b/app/data/LocalizationProcessor.test.mjs
@@ -0,0 +1,149 @@
+import { describe, expect, it } from 'vitest';
+import { LocalizationProcessor } from './LocalizationProcessor.mjs';
+
+function makeProcessor(rulesets) {
+  return new LocalizationProcessor({ code: 'en-US' }, rulesets);
+}
+
+describe('LocalizationProcessor', () => {
+  describe('filename', () => {
+    it('returns the correct path for the locale', () => {
+      const processor = makeProcessor([]);
+      expect(processor.filename).toBe('dist/data/locale/en-US.json');
+    });
+
+    it('uses the locale code', () => {
+      const processor = new LocalizationProcessor({ code: 'ja-JP' }, []);
+      expect(processor.filename).toBe('dist/data/locale/ja-JP.json');
+    });
+  });
+
+  describe('rulesetIterations', () => {
+    it('yields one entry for a simple ruleset', () => {
+      const processor = makeProcessor([
+        { key: 'stages', nodes: '$.stages.*', id: 'id', values: 'name' },
+      ]);
+
+      const results = [...processor.rulesetIterations()];
+      expect(results).toEqual([
+        { key: 'stages', node: '$.stages.*', id: 'id', value: 'name' },
+      ]);
+    });
+
+    it('yields entries for multiple nodes (array)', () => {
+      const processor = makeProcessor([
+        { key: 'weapons', nodes: ['$.main.*', '$.sub.*'], id: 'id', values: 'name' },
+      ]);
+
+      const results = [...processor.rulesetIterations()];
+      expect(results).toEqual([
+        { key: 'weapons', node: '$.main.*', id: 'id', value: 'name' },
+        { key: 'weapons', node: '$.sub.*', id: 'id', value: 'name' },
+      ]);
+    });
+
+    it('yields entries for multiple values (array)', () => {
+      const processor = makeProcessor([
+        { key: 'stages', nodes: '$.stages.*', id: 'id', values: ['name', 'description'] },
+      ]);
+
+      const results = [...processor.rulesetIterations()];
+      expect(results).toEqual([
+        { key: 'stages', node: '$.stages.*', id: 'id', value: 'name' },
+        { key: 'stages', node: '$.stages.*', id: 'id', value: 'description' },
+      ]);
+    });
+
+    it('yields cartesian product for multiple nodes and values', () => {
+      const processor = makeProcessor([
+        { key: 'items', nodes: ['$.a.*', '$.b.*'], id: 'id', values: ['name', 'desc'] },
+      ]);
+
+      const results = [...processor.rulesetIterations()];
+      expect(results).toHaveLength(4);
+      expect(results).toEqual([
+        { key: 'items', node: '$.a.*', id: 'id', value: 'name' },
+        { key: 'items', node: '$.a.*', id: 'id', value: 'desc' },
+        { key: 'items', node: '$.b.*', id: 'id', value: 'name' },
+        { key: 'items', node: '$.b.*', id: 'id', value: 'desc' },
+      ]);
+    });
+
+    it('yields entries across multiple rulesets', () => {
+      const processor = makeProcessor([
+        { key: 'stages', nodes: '$.stages.*', id: 'id', values: 'name' },
+        { key: 'weapons', nodes: '$.weapons.*', id: 'id', values: 'name' },
+      ]);
+
+      const results = [...processor.rulesetIterations()];
+      expect(results).toHaveLength(2);
+      expect(results[0].key).toBe('stages');
+      expect(results[1].key).toBe('weapons');
+    });
+  });
+
+  describe('dataIterations', () => {
+    it('yields entries with correct id, value, and path', () => {
+      const processor = makeProcessor([
+        { key: 'stages', nodes: '$.stages[*]', id: 'id', values: 'name' },
+      ]);
+
+      const data = {
+        stages: [
+          { id: 'stage-1', name: 'Scorch Gorge' },
+          { id: 'stage-2', name: 'Eeltail Alley' },
+        ],
+      };
+
+      const results = [...processor.dataIterations(data)];
+      expect(results).toHaveLength(2);
+
+      expect(results[0].id).toBe('stage-1');
+      expect(results[0].value).toBe('Scorch Gorge');
+      expect(results[0].path).toBe('stages.stage-1.name');
+
+      expect(results[1].id).toBe('stage-2');
+      expect(results[1].value).toBe('Eeltail Alley');
+      expect(results[1].path).toBe('stages.stage-2.name');
+    });
+
+    it('skips null nodes from jsonpath results', () => {
+      const processor = makeProcessor([
+        { key: 'items', nodes: '$.items[*]', id: 'id', values: 'name' },
+      ]);
+
+      const data = {
+        items: [null, { id: 'item-1', name: 'Test' }, null],
+      };
+
+      const results = [...processor.dataIterations(data)];
+      expect(results).toHaveLength(1);
+      expect(results[0].id).toBe('item-1');
+    });
+
+    it('handles nested id paths via lodash get', () => {
+      const processor = makeProcessor([
+        { key: 'gear', nodes: '$.gear[*]', id: 'meta.id', values: 'meta.name' },
+      ]);
+
+      const data = {
+        gear: [{ meta: { id: 'g-1', name: 'Splat Helmet' } }],
+      };
+
+      const results = [...processor.dataIterations(data)];
+      expect(results).toHaveLength(1);
+      expect(results[0].id).toBe('g-1');
+      expect(results[0].value).toBe('Splat Helmet');
+      expect(results[0].path).toBe('gear.g-1.meta.name');
+    });
+
+    it('returns empty for non-matching jsonpath', () => {
+      const processor = makeProcessor([
+        { key: 'stages', nodes: '$.nonexistent[*]', id: 'id', values: 'name' },
+      ]);
+
+      const results = [...processor.dataIterations({})];
+      expect(results).toHaveLength(0);
+    });
+  });
+});
diff --git a/src/common/util.test.mjs b/src/common/util.test.mjs
new file mode 100644
index 0000000..13848c5
--- /dev/null
+++ b/src/common/util.test.mjs
@@ -0,0 +1,24 @@
+import { describe, expect, it } from 'vitest';
+import { br2nl } from './util.mjs';
+
+describe('br2nl', () => {
+  it('replaces <br> with newline by default', () => {
+    expect(br2nl('hello<br>world')).toBe('hello\nworld');
+  });
+
+  it('replaces <br/> and <br /> variants', () => {
+    expect(br2nl('a<br/>b<br />c')).toBe('a\nb\nc');
+  });
+
+  it('is case-insensitive', () => {
+    expect(br2nl('a<BR>b<Br>c')).toBe('a\nb\nc');
+  });
+
+  it('uses custom replacement string when provided', () => {
+    expect(br2nl('hello<br>world', ' ')).toBe('hello world');
+  });
+
+  it('returns string unchanged when no br tags present', () => {
+    expect(br2nl('hello world')).toBe('hello world');
+  });
+});