diff --git a/.changeset/balance-commander-errors.md b/.changeset/balance-commander-errors.md
new file mode 100644
index 0000000..b410dd8
--- /dev/null
+++ b/.changeset/balance-commander-errors.md
@@ -0,0 +1,8 @@
+---
+'@offckb/cli': patch
+---
+
+Fix two CLI UX bugs reported in #498:
+
+- `offckb balance` without an address no longer leaks the SDK's `Unknown address format undefined`. The address argument is now required, so commander prints a clear `error: missing required argument 'toAddress'`.
+- Commander parameter/option errors (unknown option, invalid option value, missing argument) are printed exactly once on stderr instead of twice.
diff --git a/src/cli.ts b/src/cli.ts
index d1eb771..c02ba16 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -234,7 +234,7 @@ mainnetForkOverrideOption(
 });
 
 program
-  .command('balance [toAddress]')
+  .command('balance <toAddress>')
   .description('Check account balance (CKB + detected SUDT/xUDT), only devnet and testnet')
   .option('--network <network>', 'Specify the network to check', 'devnet')
   .addOption(new Option('--udt-kind <kind>', 'Filter by UDT kind').choices(['sudt', 'xudt']))
@@ -387,7 +387,13 @@ export async function runCli(argv: string[] = process.argv): Promise<void> {
     if (error instanceof CommanderError && error.exitCode === 0) return;
     const message = error instanceof Error ? error.message : String(error);
     const code = error instanceof CommanderError ? error.code : 'COMMAND_FAILED';
-    logger.failure(code, message);
+    // Commander errors were already written to stderr once by writeErr in
+    // configureCommanderErrors (non-JSON mode); re-emitting would duplicate
+    // the line. In JSON mode writeErr is suppressed, so logger.failure emits
+    // the single structured record instead.
+    if (!(error instanceof CommanderError) || logger.isJsonMode()) {
+      logger.failure(code, message);
+    }
     process.exitCode = error instanceof CommanderError ? error.exitCode : 1;
   }
 }
diff --git a/tests/cli-errors.test.ts b/tests/cli-errors.test.ts
new file mode 100644
index 0000000..d457a1a
--- /dev/null
+++ b/tests/cli-errors.test.ts
@@ -0,0 +1,148 @@
+const mockBalanceOf = jest.fn();
+const mockLogsCommand = jest.fn();
+const jsonMode = { value: false };
+
+jest.mock('../src/cmd/node', () => ({ startNode: jest.fn(), stopNode: jest.fn() }));
+jest.mock('../src/cmd/accounts', () => ({ accounts: jest.fn() }));
+jest.mock('../src/cmd/clean', () => ({ clean: jest.fn() }));
+jest.mock('../src/cmd/deposit', () => ({ deposit: jest.fn() }));
+jest.mock('../src/cmd/deploy', () => ({ deploy: jest.fn() }));
+jest.mock('../src/cmd/transfer', () => ({ transfer: jest.fn() }));
+jest.mock('../src/cmd/balance', () => ({ balanceOf: (...args: unknown[]) => mockBalanceOf(...args) }));
+jest.mock('../src/cmd/udt', () => ({ udtIssue: jest.fn(), udtDestroy: jest.fn() }));
+jest.mock('../src/cmd/create', () => ({ createScriptProject: jest.fn() }));
+jest.mock('../src/cmd/config', () => ({ Config: jest.fn() }));
+jest.mock('../src/cmd/devnet-config', () => ({ devnetConfig: jest.fn() }));
+jest.mock('../src/cmd/devnet-fork', () => ({ devnetFork: jest.fn() }));
+jest.mock('../src/cmd/devnet-info', () => ({ devnetInfo: jest.fn() }));
+jest.mock('../src/cmd/debug', () => ({
+  debugSingleScript: jest.fn(),
+  debugTransaction: jest.fn(),
+  parseSingleScriptOption: jest.fn(),
+}));
+jest.mock('../src/cmd/system-scripts', () => ({ printSystemScripts: jest.fn() }));
+jest.mock('../src/cmd/transfer-all', () => ({ transferAll: jest.fn() }));
+jest.mock('../src/cmd/logs', () => ({ logsCommand: (...args: unknown[]) => mockLogsCommand(...args) }));
+jest.mock('../src/cmd/status', () => ({ status: jest.fn() }));
+jest.mock('../src/scripts/gen', () => ({ genSystemScriptsJsonFile: jest.fn() }));
+jest.mock('../src/tools/ckb-debugger', () => ({ CKBDebugger: { runWithArgs: jest.fn() } }));
+
+// The logger mock mirrors the real UnifiedLogger: in JSON mode failure()
+// writes one structured record to stderr, otherwise it writes the plain
+// message to stderr like the winston console transport does. That way the
+// tests can assert each commander error reaches stderr exactly once.
+const mockFailure = jest.fn((code: string, message: string) => {
+  process.stderr.write(jsonMode.value ? `${JSON.stringify({ ok: false, code, message })}\n` : `${message}\n`);
+});
+jest.mock('../src/util/logger', () => ({
+  logger: {
+    success: jest.fn(),
+    info: jest.fn(),
+    warn: jest.fn(),
+    error: jest.fn(),
+    debug: jest.fn(),
+    result: jest.fn(),
+    failure: (...args: unknown[]) => mockFailure(args[0] as string, args[1] as string),
+    setJsonMode: (enabled: boolean) => {
+      jsonMode.value = enabled;
+    },
+    isJsonMode: () => jsonMode.value,
+    hasResult: () => false,
+  },
+}));
+
+function loadCli() {
+  jest.resetModules();
+  const cli = require('../src/cli') as typeof import('../src/cli');
+  return { runCli: cli.runCli };
+}
+
+function captureStderr() {
+  const writes: string[] = [];
+  const spy = jest.spyOn(process.stderr, 'write');
+  spy.mockImplementation(((chunk: unknown) => {
+    writes.push(String(chunk));
+    return true;
+  }) as typeof process.stderr.write);
+  return {
+    writes,
+    text: () => writes.join(''),
+    count: (needle: string) => writes.filter((w) => w.includes(needle)).length,
+    restore: () => spy.mockRestore(),
+  };
+}
+
+describe('CLI error output', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    jsonMode.value = false;
+    process.exitCode = undefined;
+  });
+
+  afterEach(() => {
+    process.exitCode = undefined;
+  });
+
+  it('balance without an address prints a clear missing-argument error once', async () => {
+    const { runCli } = loadCli();
+    const stderr = captureStderr();
+    try {
+      await runCli(['node', 'offckb', 'balance']);
+    } finally {
+      stderr.restore();
+    }
+
+    expect(stderr.count("missing required argument 'toAddress'")).toBe(1);
+    expect(stderr.text()).not.toContain('Unknown address format');
+    expect(mockBalanceOf).not.toHaveBeenCalled();
+    expect(process.exitCode).toBe(1);
+  });
+
+  it('prints an unknown-option error exactly once on stderr', async () => {
+    const { runCli } = loadCli();
+    const stderr = captureStderr();
+    try {
+      await runCli(['node', 'offckb', 'balance', 'ckt1qaddress', '--unknown-flag']);
+    } finally {
+      stderr.restore();
+    }
+
+    expect(stderr.count("unknown option '--unknown-flag'")).toBe(1);
+    expect(process.exitCode).toBe(1);
+  });
+
+  it('prints an invalid option value error exactly once on stderr', async () => {
+    const { runCli } = loadCli();
+    const stderr = captureStderr();
+    try {
+      await runCli(['node', 'offckb', 'logs', '--tail', 'abc']);
+    } finally {
+      stderr.restore();
+    }
+
+    expect(stderr.count('--tail must be a positive integer')).toBe(1);
+    expect(process.exitCode).toBe(1);
+  });
+
+  it('emits a single structured record for commander errors in JSON mode', async () => {
+    const { runCli } = loadCli();
+    const stderr = captureStderr();
+    try {
+      await runCli(['node', 'offckb', '--json', 'balance']);
+    } finally {
+      stderr.restore();
+    }
+
+    expect(stderr.count('commander.missingArgument')).toBe(1);
+    expect(stderr.text()).toContain('"ok":false');
+    expect(stderr.text()).not.toContain("error: missing required argument 'toAddress'\nerror:");
+    expect(process.exitCode).toBe(1);
+  });
+
+  it('still invokes balanceOf when an address is provided', async () => {
+    const { runCli } = loadCli();
+    await runCli(['node', 'offckb', 'balance', 'ckt1qaddress']);
+
+    expect(mockBalanceOf).toHaveBeenCalledWith('ckt1qaddress', expect.anything());
+  });
+});