diff --git a/CHANGELOG.md b/CHANGELOG.md
index 965f4ce..8f25e84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ All notable project changes are recorded here. Dates use ISO 8601 (`YYYY-MM-DD`)
 ## [Unreleased]
 
 ### Added
+- Every subcommand refuses a flag it does not accept, exits 2, and names the unknown flag and the accepted ones. Nothing runs after that refusal (#33).
 - The pre-push hook gates the commit being pushed, at that sha, in a temporary worktree. It reads the local sha from stdin and does not gate the checked-out HEAD. The base is the most recent `proofline next` pin for the task, or the parent of that commit, and a refusal prints the base it used. `proofline next --base <rev>` records a newer pin. A worktree with no evidence still gates, and stale evidence in the pushing worktree cannot block a commit that passes at its own sha (#21, #22, #23).
 - `proofline contract sign` writes `proofline.json.sig`, a signature over the canonical contract by the agentkey owner role. `proofline contract verify-sig` checks it against `guard/owner.pub` only. Once that pin is present, `next`, `verify`, `gate`, `brief` and both hooks exit 2 with `contract not owner-signed` when the signature is missing, altered or from another key. `proofline contract propose` writes `proposals/<sha256>.diff` and prints the hash.
 - `proofline setup` installs the hooks, creates the owner key through agentkey and sets approvals to `.proofline/approvals`. `proofline task` writes a proposal from plain words and prints its hash. `proofline contract approve` shows the diff and, on y, writes the marker and applies the bytes. `proofline watch` prints the active task until the gate is PASS.
diff --git a/bin/proofline.mjs b/bin/proofline.mjs
index d4c3b7f..8d3dbbf 100755
--- a/bin/proofline.mjs
+++ b/bin/proofline.mjs
@@ -75,8 +75,55 @@ const HELP = `proofline: independent V&V and delivery controller
   mcp                                   MCP server on stdio
 Global: --json  --root <dir>   Exit: 0 PASS, 1 FAIL, 2 BLOCKED, 3 usage`;
 
+const GLOBAL_FLAGS = ['json', 'root'];
+const ACCEPTED_FLAGS = {
+  setup: ['agent'],
+  task: [],
+  init: ['approvals', 'no-hooks'],
+  'contract create': ['from', 'id', 'title', 'phase', 'owner', 'description', 'depends', 'scope'],
+  'contract merge': ['owners'],
+  'contract coverage': ['contracts'],
+  'contract scaffold': ['title', 'scope', 'kind', 'id'],
+  'contract approve': [],
+  'contract sign': [],
+  'contract verify-sig': [],
+  'contract propose': [],
+  'contract validate': ['base'],
+  'contract show': [],
+  next: ['owner', 'base'],
+  brief: ['owner', 'base'],
+  verify: ['claims', 'claims-file', 'base', 'fresh'],
+  gate: ['claims', 'claims-file', 'base', 'fresh', 'all', 'ci', 'skip-pushed'],
+  report: [],
+  status: ['owner'],
+  'evidence record': ['data'],
+  'evidence verify': [],
+  'evidence log': [],
+  'verify-receipt': ['keys', 'sigstore', 'recompute', 'base'],
+  receipt: ['base', 'role', 'task', 'vault'],
+  hook: [],
+  watch: [],
+  connect: [],
+  mcp: [],
+};
+
+function refuseUnknownFlags(cmd, sub) {
+  if (!cmd) return;
+  const key = sub ? `${cmd} ${sub}` : cmd;
+  const accepted = ACCEPTED_FLAGS[key] ?? ACCEPTED_FLAGS[cmd];
+  if (!accepted) return;
+  const allow = new Set([...GLOBAL_FLAGS, ...accepted]);
+  const bad = Object.keys(flags).filter((k) => !allow.has(k));
+  if (!bad.length) return;
+  const named = bad.map((k) => `--${k}`).join(', ');
+  const ok = [...allow].sort().map((k) => `--${k}`).join(', ');
+  console.error(`proofline: unknown flag ${named}\naccepted: ${ok}`);
+  process.exit(2);
+}
+
 try {
   const [cmd, sub] = pos;
+  refuseUnknownFlags(cmd, sub);
   switch (cmd) {
     case 'setup': {
       const agent = flags.agent === undefined ? 'none' : flags.agent;
diff --git a/test/cli_unknown_flags.test.mjs b/test/cli_unknown_flags.test.mjs
new file mode 100644
index 0000000..72c9516
--- /dev/null
+++ b/test/cli_unknown_flags.test.mjs
@@ -0,0 +1,70 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { spawnSync } from 'node:child_process';
+import { BIN, repo } from './helpers.mjs';
+
+const run = (args, cwd) => spawnSync(process.execPath, [BIN, ...args], {
+  cwd, encoding: 'utf8', timeout: 2000,
+});
+
+const COMMANDS = [
+  ['setup'],
+  ['task', 'plain words'],
+  ['init'],
+  ['contract', 'create'],
+  ['contract', 'merge'],
+  ['contract', 'coverage'],
+  ['contract', 'scaffold'],
+  ['contract', 'approve'],
+  ['contract', 'sign'],
+  ['contract', 'verify-sig'],
+  ['contract', 'propose'],
+  ['contract', 'validate'],
+  ['contract', 'show'],
+  ['next'],
+  ['brief'],
+  ['verify'],
+  ['gate'],
+  ['report'],
+  ['status'],
+  ['evidence', 'record'],
+  ['evidence', 'verify'],
+  ['evidence', 'log'],
+  ['verify-receipt'],
+  ['receipt'],
+  ['hook'],
+  ['watch'],
+  ['connect'],
+  ['mcp'],
+];
+
+test('contract validate --file exits 2 and names the flag', () => {
+  const r = repo();
+  const res = run(['contract', 'validate', '--file', '/tmp/does-not-exist-proposal.json', '--root', r], r);
+  assert.equal(res.status, 2, res.stderr);
+  assert.match(res.stderr, /unknown flag --file/);
+  assert.match(res.stderr, /accepted:/);
+  assert.doesNotMatch(`${res.stdout}\n${res.stderr}`, /warning:/);
+});
+
+test('an unknown flag on each subcommand exits 2 and names the flag', () => {
+  const r = repo();
+  for (const args of COMMANDS) {
+    const res = run([...args, '--not-a-real-flag', '--root', r], r);
+    assert.equal(res.status, 2, `${args.join(' ')} ${res.stderr}`);
+    assert.match(res.stderr, /unknown flag --not-a-real-flag/);
+    assert.match(res.stderr, /accepted:/);
+  }
+});
+
+test('accepted flags still run the command', () => {
+  const r = repo();
+  const validate = run(['contract', 'validate', '--root', r], r);
+  assert.notEqual(validate.status, 2, validate.stderr);
+  const shown = run(['contract', 'scaffold', '--title', 'A task', '--scope', 'src', '--root', r], r);
+  assert.equal(shown.status, 0, shown.stderr);
+  assert.match(shown.stdout, /"title": "A task"/);
+  const status = run(['status', '--json', '--root', r], r);
+  assert.notEqual(status.status, 2, status.stderr);
+  assert.doesNotThrow(() => JSON.parse(status.stdout));
+});