diff --git a/ckcc/cli.py b/ckcc/cli.py
index eade658..b6f3987 100755
--- a/ckcc/cli.py
+++ b/ckcc/cli.py
@@ -463,6 +463,129 @@ def sign_message(message, path, verbose, just_sig, wrap, segwit):
             click.echo('%s\n%s\n%s' % (message.decode('ascii'), addr, sig))
 
 
+@main.command('msg-file')
+@click.argument('json_file', type=click.Path(exists=True, dir_okay=False), metavar="FILE_PATH")
+@click.option('--outfile', '-o', type=click.Path(), default=None,
+              help="Output file path for signed result (default: <basename>-signed.<ext>)")
+@click.option('--outdir', '-d', type=click.Path(exists=True, dir_okay=True, file_okay=False),
+              default=None, help="Directory to save signed file (default: same as input)")
+def sign_msg_file(json_file, outfile, outdir):
+    """
+    Sign a text file containing a message (TXT or JSON format).
+
+    Reads a JSON or TXT file, extracts the message to sign, sends it to the Coldcard
+    for signing, and writes the result as an RFC2440-like signed message file.
+
+    For JSON files, the file must contain a 'msg' field. The 'subpath' and 'addr_fmt'
+    fields are optional:
+
+        {"msg":"this address belongs to me","subpath":"m/84h/0h/0h/0/120"}
+
+    For TXT files, the first line is the message. The optional second line specifies
+    the subkey derivation path. The optional third line specifies the address format
+    (p2pkh, p2sh-p2wpkh, or p2wpkh).
+
+    The signed output file is saved with '-signed' inserted before the file extension.
+    """
+
+    basename = os.path.basename(json_file)
+    name, ext = os.path.splitext(basename)
+    ext_lower = ext.lower()
+
+    if ext_lower not in ('.txt', '.json'):
+        click.echo("Error: file must have .txt or .json extension")
+        sys.exit(1)
+
+    if '-signed' in name:
+        click.echo("Error: filename cannot contain '-signed'")
+        sys.exit(1)
+
+    raw = open(json_file, 'r').read()
+    if len(raw.encode('utf-8')) > 500: #CC Spec: "Be less than 500 bytes in size"
+        click.echo("Error: file must be less than 500 bytes")
+        sys.exit(1)
+
+    # parse file contents
+    message = None
+    subpath = None
+    addr_fmt_str = None
+
+    try:
+        parsed = json.loads(raw)
+        if isinstance(parsed, dict):
+            if 'msg' not in parsed:
+                click.echo("Error: JSON must contain 'msg' field")
+                sys.exit(1)
+            message = parsed['msg']
+            subpath = parsed.get('subpath', None)
+            addr_fmt_str = parsed.get('addr_fmt', None)
+        else:
+            raise ValueError("not a JSON object")
+    except (json.JSONDecodeError, ValueError):
+        lines = raw.strip().split('\n')
+        if not lines or not lines[0].strip():
+            click.echo("Error: file is empty or has no message")
+            sys.exit(1)
+        message = lines[0].strip()
+        if len(lines) >= 2 and lines[1].strip():
+            subpath = lines[1].strip()
+        if len(lines) >= 3 and lines[2].strip():
+            addr_fmt_str = lines[2].strip()
+
+    wrap = False
+    segwit = False
+    if addr_fmt_str:
+        af = addr_fmt_str.lower().replace('-', '').replace('_', '')
+        if af in ('p2shp2wpkh', 'p2sh_p2wpkh', 'p2shp2wpkh'):
+            wrap = True
+        elif af in ('p2wpkh', 'segwit', 'bech32'):
+            segwit = True
+        elif af not in ('p2pkh', 'classic', ''):
+            click.echo("Warning: unknown addr_fmt '%s', using default (p2pkh)" % addr_fmt_str,
+                        err=True)
+
+    with get_device() as dev:
+
+        addr_fmt, af_path = addr_fmt_help(dev, wrap, segwit)
+        signing_path = subpath or af_path
+        msg_bytes = message.encode('ascii') if not isinstance(message, bytes) else message
+
+        ok = dev.send_recv(CCProtocolPacker.sign_message(msg_bytes, signing_path, addr_fmt),
+                           timeout=None)
+        assert ok == None
+
+        print("Waiting for OK on the Coldcard...", end='', file=sys.stderr)
+        sys.stderr.flush()
+
+        while 1:
+            time.sleep(0.250)
+            done = dev.send_recv(CCProtocolPacker.get_signed_msg(), timeout=None)
+            if done == None:
+                continue
+            break
+
+        print("\r                                  \r", end='', file=sys.stderr)
+        sys.stderr.flush()
+
+        if len(done) != 2:
+            click.echo('Failed: %r' % done)
+            sys.exit(1)
+
+        addr, raw_sig = done
+
+        sig = str(b64encode(raw_sig), 'ascii').replace('\n', '')
+
+        # format as RFC2440-like armoured output
+        result = RFC_SIGNATURE_TEMPLATE.format(msg=message, addr=addr, sig=sig)
+
+        if not outfile:
+            out_dir = outdir or os.path.dirname(os.path.abspath(json_file))
+            signed_name = '%s-signed%s' % (name, ext)
+            outfile = os.path.join(out_dir, signed_name)
+
+        open(outfile, 'w').write(result)
+        click.echo("Wrote signed message to: %s" % outfile)
+
 def wait_and_download(dev, req, fn):
     # Wait for user action on the device... by polling w/ indicated request
     # - also download resulting file