diff --git a/src/plugins/built-in/writing-studio/snapshot-manager.js b/src/plugins/built-in/writing-studio/snapshot-manager.js
new file mode 100644
index 0000000..7b174d7
--- /dev/null
+++ b/src/plugins/built-in/writing-studio/snapshot-manager.js
@@ -0,0 +1,73 @@
+class SnapshotManager {
+  /**
+   * @param {object} store - { get(key), set(key, value) }
+   * @param {string} storeKey - settings key for snapshots
+   */
+  constructor(store, storeKey = 'plugins.writing-studio.snapshots') {
+    this.store = store;
+    this.storeKey = storeKey;
+  }
+
+  _getAll() {
+    const raw = this.store.get(this.storeKey);
+    return raw ? JSON.parse(raw) : [];
+  }
+
+  _saveAll(snaps) {
+    this.store.set(this.storeKey, JSON.stringify(snaps));
+  }
+
+  create(content, label = 'manual') {
+    const snaps = this._getAll();
+    const snap = {
+      id: 'snap-' + Date.now() + '-' + Math.random().toString(36).slice(2, 8),
+      timestamp: new Date().toISOString(),
+      content,
+      wordCount: content.split(/\s+/).filter(Boolean).length,
+      label
+    };
+    snaps.unshift(snap);
+    this._saveAll(snaps);
+    return snap;
+  }
+
+  list() {
+    return this._getAll();
+  }
+
+  getById(id) {
+    return this._getAll().find(s => s.id === id) || null;
+  }
+
+  restore(id) {
+    const snap = this.getById(id);
+    if (!snap) throw new Error('Snapshot not found');
+    return snap.content;
+  }
+
+  delete(id) {
+    const snaps = this._getAll().filter(s => s.id !== id);
+    this._saveAll(snaps);
+  }
+
+  diff(id, currentContent) {
+    const snap = this.getById(id);
+    if (!snap) throw new Error('Snapshot not found');
+    const oldLines = snap.content.split('\n');
+    const newLines = currentContent.split('\n');
+    const oldSet = new Set(oldLines);
+    const newSet = new Set(newLines);
+    let added = 0;
+    let removed = 0;
+    for (const line of newLines) { if (!oldSet.has(line)) added++; }
+    for (const line of oldLines) { if (!newSet.has(line)) removed++; }
+    return { added, removed };
+  }
+
+  prune(keepCount) {
+    const snaps = this._getAll();
+    this._saveAll(snaps.slice(0, keepCount));
+  }
+}
+
+module.exports = { SnapshotManager };
diff --git a/tests/snapshot-manager.test.js b/tests/snapshot-manager.test.js
new file mode 100644
index 0000000..56e930e
--- /dev/null
+++ b/tests/snapshot-manager.test.js
@@ -0,0 +1,73 @@
+const { SnapshotManager } = require('../src/plugins/built-in/writing-studio/snapshot-manager');
+
+describe('SnapshotManager', () => {
+  let manager;
+  let store;
+
+  beforeEach(() => {
+    store = {};
+    manager = new SnapshotManager({
+      get: (key) => store[key],
+      set: (key, value) => { store[key] = value; }
+    });
+  });
+
+  test('create stores snapshot with timestamp, content, wordCount', () => {
+    const snap = manager.create('Hello world this is a test', 'auto');
+    expect(snap).toHaveProperty('id');
+    expect(snap.content).toBe('Hello world this is a test');
+    expect(snap.wordCount).toBe(6);
+    expect(snap.label).toBe('auto');
+  });
+
+  test('list returns snapshots ordered newest first', () => {
+    manager.create('first', 'auto');
+    manager.create('second', 'auto');
+    const list = manager.list();
+    expect(list.length).toBe(2);
+    expect(list[0].content).toBe('second');
+  });
+
+  test('getById returns specific snapshot', () => {
+    const snap = manager.create('find me', 'manual');
+    const found = manager.getById(snap.id);
+    expect(found.content).toBe('find me');
+  });
+
+  test('getById returns null for missing id', () => {
+    expect(manager.getById('nope')).toBeNull();
+  });
+
+  test('restore returns content of snapshot', () => {
+    const snap = manager.create('restore this', 'manual');
+    expect(manager.restore(snap.id)).toBe('restore this');
+  });
+
+  test('restore throws for missing snapshot', () => {
+    expect(() => manager.restore('nope')).toThrow('Snapshot not found');
+  });
+
+  test('delete removes a snapshot', () => {
+    const snap = manager.create('delete me', 'auto');
+    manager.delete(snap.id);
+    expect(manager.getById(snap.id)).toBeNull();
+  });
+
+  test('diff returns added/removed line counts', () => {
+    const snap = manager.create('line one\nline two\nline three', 'auto');
+    const result = manager.diff(snap.id, 'line one\nline modified\nline three\nline four');
+    expect(result.added).toBe(2);
+    expect(result.removed).toBe(1);
+  });
+
+  test('diff throws for missing snapshot', () => {
+    expect(() => manager.diff('nope', 'new content')).toThrow('Snapshot not found');
+  });
+
+  test('prune keeps only the N most recent snapshots', () => {
+    for (let i = 0; i < 10; i++) manager.create('snap ' + i, 'auto');
+    manager.prune(5);
+    expect(manager.list().length).toBe(5);
+    expect(manager.list()[0].content).toBe('snap 9');
+  });
+});