diff --git a/src/index.ts b/src/index.ts
index 7a24d5b..a1eac2b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -22,7 +22,7 @@ Commands
   doctor      Fire a test payload through the hook to prove it is wired
   verify      Exit non-zero if a decoy was read or a canary leaked
   clean       Remove planted decoys and unregister the hook
-  hook           Internal: read a PreToolUse payload on stdin and judge it
+  hook           Internal: read a tool-call hook payload on stdin and judge it
   session-start  Internal: report outstanding trips at the start of a session
 
 Options
@@ -36,6 +36,28 @@ Options
 Docs: https://github.com/aiagentflow/canaryhook
 `;
 
+/** Flags each command accepts beyond --json, -h and -v. */
+const FLAGS: Record<string, string[]> = {
+  init: ["--commit", "--force"],
+  clean: ["--keep-alerts"],
+  status: [],
+  alerts: [],
+  doctor: [],
+  verify: [],
+};
+
+/**
+ * A mistyped flag would otherwise be ignored, so `init --froce` reports
+ * "already initialized" and `clean --keep-alert` deletes the record it meant
+ * to keep. The internal hook commands are left out: a hook must never fail.
+ */
+function unknownArg(command: string, args: string[]): string | null {
+  const allowed = FLAGS[command];
+  if (allowed === undefined) return null;
+  const known = new Set([...allowed, "--json", "-h", "--help", "-v", "--version"]);
+  return args.find((arg) => (arg.startsWith("-") ? !known.has(arg) : arg !== command)) ?? null;
+}
+
 async function main(argv: string[]): Promise<number> {
   const args = argv.slice(2);
   const has = (flag: string) => args.includes(flag);
@@ -54,6 +76,12 @@ async function main(argv: string[]): Promise<number> {
     return 0;
   }
 
+  const unknown = unknownArg(command, args);
+  if (unknown !== null) {
+    process.stderr.write(`Unknown option for ${command}: ${unknown}\n\n${HELP}`);
+    return 1;
+  }
+
   switch (command) {
     case "hook":
       return runHook();
diff --git a/test/root.test.js b/test/root.test.js
index f4ebe49..a2f726c 100644
--- a/test/root.test.js
+++ b/test/root.test.js
@@ -85,3 +85,12 @@ test("verify passes a fresh install with no trips", () => {
   const { root } = project();
   assert.equal(run(["verify"], root).status, 0);
 });
+
+test("rejects a mistyped flag instead of ignoring it", () => {
+  const { root } = project();
+  const result = run(["clean", "--keep-alert"], root);
+  assert.equal(result.status, 1);
+  assert.match(result.stderr, /Unknown option for clean: --keep-alert/);
+  assert.equal(run(["status", "extra"], root).status, 1);
+  assert.equal(run(["status", "--json"], root).status, 0);
+});