diff --git a/TODO b/TODO
index 4686732..1fad08e 100644
--- a/TODO
+++ b/TODO
@@ -203,7 +203,7 @@ Content-Type: application/issue
 ID: 13
 Type: feature
 Title: implement browser local storage handler
-Status: open
+Status: done
 Priority: medium
 Created: 2026-03-13
 Relationships: dependsOn:8
diff --git a/src/handler.ts b/src/handler.ts
index e174133..6f66f50 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -219,6 +219,114 @@ export class FileHandler extends StreamHandler {
     }
 }
 
+/**
+ * A handler that persists log records to browser localStorage.
+ *
+ * Records are stored as a JSON array of formatted strings under a
+ * configurable key. Log rotation is supported by entry count and/or
+ * byte size to avoid exceeding storage quotas.
+ */
+export interface LocalStorageHandlerOptions {
+    /**
+     * localStorage key to store entries under.
+     * Defaults to 'esm-logging'.
+     */
+    key?: string;
+
+    /**
+     * Maximum number of entries to retain. Oldest entries are discarded
+     * first. Set to 0 for no entry limit. Defaults to 1000.
+     */
+    maxEntries?: number;
+
+    /**
+     * Maximum size in bytes (as measured by the JSON-serialized string
+     * length). Oldest entries are discarded to stay within this limit.
+     * Set to 0 for no byte limit. Defaults to 0.
+     */
+    maxBytes?: number;
+}
+
+export class LocalStorageHandler extends Handler {
+    protected key: string;
+    protected maxEntries: number;
+    protected maxBytes: number;
+
+    constructor(options?: LocalStorageHandlerOptions) {
+        super();
+
+        if (typeof localStorage === 'undefined') {
+            throw new NotImplementedError(
+                'LocalStorageHandler requires a browser environment with localStorage'
+            );
+        }
+
+        this.key = options?.key ?? 'esm-logging';
+        this.maxEntries = options?.maxEntries ?? 1000;
+        this.maxBytes = options?.maxBytes ?? 0;
+    }
+
+    emit(record: LogRecord) {
+        try {
+            const msg = this.format(record);
+            const entries = this.getEntries();
+            entries.push(msg);
+            this._rotate(entries);
+            this._setEntries(entries);
+        }
+        catch (e) {
+            this.handleError(record);
+        }
+    }
+
+    /**
+     * Retrieve all stored log entries.
+     */
+    getEntries(): string[] {
+        try {
+            const data = localStorage.getItem(this.key);
+            return data ? JSON.parse(data) : [];
+        }
+        catch {
+            return [];
+        }
+    }
+
+    /**
+     * Remove all stored log entries.
+     */
+    clearEntries() {
+        localStorage.removeItem(this.key);
+    }
+
+    close() {
+        super.close();
+    }
+
+    /**
+     * Discard oldest entries to stay within maxEntries and maxBytes limits.
+     */
+    protected _rotate(entries: string[]) {
+        if (this.maxEntries > 0) {
+            while (entries.length > this.maxEntries) {
+                entries.shift();
+            }
+        }
+
+        if (this.maxBytes > 0) {
+            while (entries.length > 0) {
+                const serialized = JSON.stringify(entries);
+                if (serialized.length <= this.maxBytes) { break }
+                entries.shift();
+            }
+        }
+    }
+
+    protected _setEntries(entries: string[]) {
+        localStorage.setItem(this.key, JSON.stringify(entries));
+    }
+}
+
 /**
  * This class is like a StreamHandler using sys.stderr, but always uses
  * whatever sys.stderr is currently set to rather than the value of
diff --git a/tests/unit/local-storage-handler.test.ts b/tests/unit/local-storage-handler.test.ts
new file mode 100644
index 0000000..a00b701
--- /dev/null
+++ b/tests/unit/local-storage-handler.test.ts
@@ -0,0 +1,158 @@
+import {expect, jest, test, beforeEach, afterEach} from '@jest/globals';
+import { LocalStorageHandler } from '../../src/handler';
+import { LogRecord } from '../../src/log-record';
+import { DEBUG, WARNING, ERROR } from '../../src/log-level';
+
+// mock localStorage for Node/Jest environment
+const store: {[key: string]: string} = {};
+const localStorageMock = {
+    getItem: (key: string): string | null => store[key] ?? null,
+    setItem: (key: string, value: string) => { store[key] = value },
+    removeItem: (key: string) => { delete store[key] },
+};
+
+function clearStore() {
+    for (const key of Object.keys(store)) { delete store[key] }
+}
+
+function makeRecord(level: number, msg: string): LogRecord {
+    return new LogRecord('test', { level, msg });
+}
+
+beforeEach(() => {
+    clearStore();
+    (globalThis as any).localStorage = localStorageMock;
+});
+
+afterEach(() => {
+    clearStore();
+    delete (globalThis as any).localStorage;
+});
+
+describe('LocalStorageHandler', () => {
+    describe('constructor', () => {
+        test('uses default key and limits', () => {
+            const h = new LocalStorageHandler();
+            expect(h.getEntries()).toEqual([]);
+        });
+
+        test('throws when localStorage is unavailable', () => {
+            delete (globalThis as any).localStorage;
+            expect(() => new LocalStorageHandler()).toThrow(
+                'requires a browser environment'
+            );
+        });
+
+        test('accepts custom options', () => {
+            const h = new LocalStorageHandler({
+                key: 'custom-log',
+                maxEntries: 50,
+                maxBytes: 4096,
+            });
+            h.emit(makeRecord(DEBUG, 'test'));
+            expect(store['custom-log']).toBeDefined();
+            expect(store['esm-logging']).toBeUndefined();
+        });
+    });
+
+    describe('emit', () => {
+        test('stores formatted log entry', () => {
+            const h = new LocalStorageHandler();
+            h.emit(makeRecord(WARNING, 'hello'));
+            const entries = h.getEntries();
+            expect(entries.length).toBe(1);
+            expect(entries[0]).toContain('hello');
+        });
+
+        test('appends multiple entries', () => {
+            const h = new LocalStorageHandler();
+            h.emit(makeRecord(DEBUG, 'first'));
+            h.emit(makeRecord(DEBUG, 'second'));
+            h.emit(makeRecord(DEBUG, 'third'));
+            expect(h.getEntries().length).toBe(3);
+        });
+
+        test('persists across handler instances with same key', () => {
+            const h1 = new LocalStorageHandler({ key: 'shared' });
+            h1.emit(makeRecord(DEBUG, 'from h1'));
+
+            const h2 = new LocalStorageHandler({ key: 'shared' });
+            const entries = h2.getEntries();
+            expect(entries.length).toBe(1);
+            expect(entries[0]).toContain('from h1');
+        });
+    });
+
+    describe('rotation by entry count', () => {
+        test('discards oldest entries when maxEntries exceeded', () => {
+            const h = new LocalStorageHandler({ maxEntries: 3 });
+            h.emit(makeRecord(DEBUG, 'msg-1'));
+            h.emit(makeRecord(DEBUG, 'msg-2'));
+            h.emit(makeRecord(DEBUG, 'msg-3'));
+            h.emit(makeRecord(DEBUG, 'msg-4'));
+
+            const entries = h.getEntries();
+            expect(entries.length).toBe(3);
+            expect(entries[0]).toContain('msg-2');
+            expect(entries[2]).toContain('msg-4');
+        });
+
+        test('maxEntries of 1 keeps only the latest', () => {
+            const h = new LocalStorageHandler({ maxEntries: 1 });
+            h.emit(makeRecord(DEBUG, 'old'));
+            h.emit(makeRecord(DEBUG, 'new'));
+
+            const entries = h.getEntries();
+            expect(entries.length).toBe(1);
+            expect(entries[0]).toContain('new');
+        });
+    });
+
+    describe('rotation by byte size', () => {
+        test('discards oldest entries when maxBytes exceeded', () => {
+            const h = new LocalStorageHandler({ maxEntries: 0, maxBytes: 100 });
+            // emit entries until we exceed the limit
+            for (let i = 0; i < 20; i++) {
+                h.emit(makeRecord(DEBUG, `message-${i}`));
+            }
+
+            const entries = h.getEntries();
+            const serialized = JSON.stringify(entries);
+            expect(serialized.length).toBeLessThanOrEqual(100);
+            expect(entries.length).toBeGreaterThan(0);
+        });
+    });
+
+    describe('getEntries', () => {
+        test('returns empty array when no entries', () => {
+            const h = new LocalStorageHandler();
+            expect(h.getEntries()).toEqual([]);
+        });
+
+        test('returns empty array on corrupt data', () => {
+            store['esm-logging'] = 'not valid json{{{';
+            const h = new LocalStorageHandler();
+            expect(h.getEntries()).toEqual([]);
+        });
+    });
+
+    describe('clearEntries', () => {
+        test('removes all stored entries', () => {
+            const h = new LocalStorageHandler();
+            h.emit(makeRecord(DEBUG, 'to be cleared'));
+            expect(h.getEntries().length).toBe(1);
+
+            h.clearEntries();
+            expect(h.getEntries()).toEqual([]);
+        });
+    });
+
+    describe('close', () => {
+        test('sets closed to true', () => {
+            const h = new LocalStorageHandler();
+            expect(h.closed).toBe(false);
+            h.close();
+            expect(h.closed).toBe(true);
+        });
+    });
+});