diff --git a/src/plugins/plugin-loader.js b/src/plugins/plugin-loader.js
new file mode 100644
index 0000000..4334b05
--- /dev/null
+++ b/src/plugins/plugin-loader.js
@@ -0,0 +1,75 @@
+const fs = require('fs');
+const path = require('path');
+
+class PluginLoader {
+  /**
+   * @param {string[]} searchDirs - Directories to scan for plugin folders
+   */
+  constructor(searchDirs = []) {
+    this.searchDirs = searchDirs;
+    this.loadedIds = new Set();
+  }
+
+  /**
+   * Discover plugins by scanning searchDirs for manifest.json files.
+   * Returns array of { id, name, version, description, manifest, PluginClass, dir }
+   */
+  discoverPlugins() {
+    const plugins = [];
+    for (const dir of this.searchDirs) {
+      if (!fs.existsSync(dir)) continue;
+      const entries = fs.readdirSync(dir, { withFileTypes: true });
+      for (const entry of entries) {
+        if (!entry.isDirectory()) continue;
+        const pluginDir = path.join(dir, entry.name);
+        const manifestPath = path.join(pluginDir, 'manifest.json');
+        if (!fs.existsSync(manifestPath)) continue;
+        try {
+          const raw = fs.readFileSync(manifestPath, 'utf-8');
+          const manifest = JSON.parse(raw);
+          this.validateManifest(manifest);
+          let PluginClass = null;
+          const indexPath = path.join(pluginDir, 'index.js');
+          if (fs.existsSync(indexPath)) {
+            try {
+              const loaded = require(indexPath);
+              PluginClass = loaded.Plugin || loaded.default || null;
+            } catch (err) {
+              console.error(`[PluginLoader] Failed to load index.js for "${manifest.id}":`, err.message);
+              continue;
+            }
+          }
+          plugins.push({
+            id: manifest.id,
+            name: manifest.name,
+            version: manifest.version,
+            description: manifest.description,
+            manifest,
+            PluginClass,
+            dir: pluginDir
+          });
+          this.loadedIds.add(manifest.id);
+        } catch (err) {
+          console.error(`[PluginLoader] Skipping plugin in ${pluginDir}:`, err.message);
+        }
+      }
+    }
+    return plugins;
+  }
+
+  /**
+   * Validate a manifest object. Throws on invalid.
+   */
+  validateManifest(manifest) {
+    if (!manifest.id) throw new Error('Manifest missing required field: id');
+    if (!manifest.name) throw new Error('Manifest missing required field: name');
+    if (!manifest.version) throw new Error('Manifest missing required field: version');
+    if (!manifest.description) throw new Error('Manifest missing required field: description');
+    if (this.loadedIds.has(manifest.id)) {
+      throw new Error(`Duplicate plugin id: "${manifest.id}"`);
+    }
+    return true;
+  }
+}
+
+module.exports = { PluginLoader };
diff --git a/tests/plugin-loader.test.js b/tests/plugin-loader.test.js
new file mode 100644
index 0000000..ed4ce7b
--- /dev/null
+++ b/tests/plugin-loader.test.js
@@ -0,0 +1,102 @@
+const path = require('path');
+const fs = require('fs');
+const os = require('os');
+const { PluginLoader } = require('../src/plugins/plugin-loader');
+
+describe('PluginLoader', () => {
+  let tempDir;
+
+  beforeEach(() => {
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'plugin-test-'));
+  });
+
+  afterEach(() => {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  });
+
+  function writeManifest(dir, manifest) {
+    fs.mkdirSync(dir, { recursive: true });
+    fs.writeFileSync(path.join(dir, 'manifest.json'), JSON.stringify(manifest, null, 2));
+  }
+
+  test('discoverPlugins — finds manifests in built-in directory', () => {
+    const pluginDir = path.join(tempDir, 'my-plugin');
+    writeManifest(pluginDir, {
+      id: 'my-plugin',
+      name: 'My Plugin',
+      version: '1.0.0',
+      description: 'Test'
+    });
+    const loader = new PluginLoader([tempDir]);
+    const plugins = loader.discoverPlugins();
+    expect(plugins).toHaveLength(1);
+    expect(plugins[0].id).toBe('my-plugin');
+  });
+
+  test('discoverPlugins — skips directories without manifest.json', () => {
+    const emptyDir = path.join(tempDir, 'no-manifest');
+    fs.mkdirSync(emptyDir, { recursive: true });
+    const loader = new PluginLoader([emptyDir]);
+    const plugins = loader.discoverPlugins();
+    expect(plugins).toHaveLength(0);
+  });
+
+  test('validateManifest — accepts valid manifest', () => {
+    const manifest = {
+      id: 'test-plugin',
+      name: 'Test Plugin',
+      version: '1.0.0',
+      description: 'A test plugin'
+    };
+    const loader = new PluginLoader([]);
+    expect(loader.validateManifest(manifest)).toBe(true);
+  });
+
+  test('validateManifest — rejects manifest missing id', () => {
+    const manifest = { name: 'No ID', version: '1.0.0', description: 'x' };
+    const loader = new PluginLoader([]);
+    expect(() => loader.validateManifest(manifest)).toThrow(/id/);
+  });
+
+  test('validateManifest — rejects manifest missing name', () => {
+    const manifest = { id: 'test', version: '1.0.0', description: 'x' };
+    const loader = new PluginLoader([]);
+    expect(() => loader.validateManifest(manifest)).toThrow(/name/);
+  });
+
+  test('validateManifest — rejects manifest with duplicate id', () => {
+    const loader = new PluginLoader([]);
+    loader.loadedIds = new Set(['existing-plugin']);
+    expect(() => loader.validateManifest({ id: 'existing-plugin', name: 'Dup', version: '1.0.0', description: 'x' }))
+      .toThrow(/duplicate/i);
+  });
+
+  test('discoverPlugins — loads index.js Plugin export if present', () => {
+    const pluginDir = path.join(tempDir, 'with-index');
+    writeManifest(pluginDir, { id: 'with-index', name: 'With Index', version: '1.0.0', description: 'Test' });
+    // Write a simple index.js with a Plugin export
+    fs.writeFileSync(path.join(pluginDir, 'index.js'), `
+class SimplePlugin { init() {} }
+module.exports = { Plugin: SimplePlugin };
+`);
+    const loader = new PluginLoader([tempDir]);
+    const plugins = loader.discoverPlugins();
+    expect(plugins).toHaveLength(1);
+    expect(plugins[0].PluginClass).toBeDefined();
+    expect(plugins[0].PluginClass.name).toBe('SimplePlugin');
+  });
+
+  test('discoverPlugins — continues if one plugin fails to load', () => {
+    const badDir = path.join(tempDir, 'bad');
+    writeManifest(badDir, { id: 'bad', name: 'Bad', version: '1.0.0', description: 'Broken' });
+    fs.writeFileSync(path.join(badDir, 'index.js'), 'throw new Error("broken");');
+
+    const goodDir = path.join(tempDir, 'good');
+    writeManifest(goodDir, { id: 'good', name: 'Good', version: '1.0.0', description: 'Works' });
+
+    const loader = new PluginLoader([tempDir]);
+    const plugins = loader.discoverPlugins();
+    expect(plugins).toHaveLength(1);
+    expect(plugins[0].id).toBe('good');
+  });
+});