MANIFEST                       |  1 +
 lib/PublicInbox/LEI.pm         |  2 ++
 lib/PublicInbox/LeiExternal.pm |  2 +-
 lib/PublicInbox/LeiLsSync.pm   | 29 +++++++++++++++++++++++++++++
 t/lei-import-imap.t            |  2 ++
 t/lei-import-maildir.t         |  3 +++

diff --git a/MANIFEST b/MANIFEST
index ce824fcf3276cfc8792085ee6e385430a4fad94d..d4e7d66f9f1b0e63bfaf3d6925159a8732eac542 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -202,6 +202,7 @@ lib/PublicInbox/LeiInput.pm
 lib/PublicInbox/LeiInspect.pm
 lib/PublicInbox/LeiLsLabel.pm
 lib/PublicInbox/LeiLsSearch.pm
+lib/PublicInbox/LeiLsSync.pm
 lib/PublicInbox/LeiMailSync.pm
 lib/PublicInbox/LeiMirror.pm
 lib/PublicInbox/LeiOverview.pm
diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index 39278de640a0ab9004597d281ae3484caa18b140..c170572bb919d10588961adef7b64b1ce0f54e9e 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -161,6 +161,8 @@ 	PublicInbox::LeiQuery::curl_opt() ],
 'ls-external' => [ '[FILTER]', 'list publicinbox|extindex locations',
 	qw(format|f=s z|0 globoff|g invert-match|v local remote), @c_opt ],
 'ls-label' => [ '', 'list labels', qw(z|0 stats:s), @c_opt ],
+'ls-sync' => [ '', 'list sync folders',
+		qw(z|0 z|0 globoff|g invert-match|v local remote), @c_opt ],
 'forget-external' => [ 'LOCATION...|--prune',
 	'exclude further results from a publicinbox|extindex',
 	qw(prune), @c_opt ],
diff --git a/lib/PublicInbox/LeiExternal.pm b/lib/PublicInbox/LeiExternal.pm
index b0ebe9479b6254294fada399d746933484a7d6e2..3858085ece8cc0c04e49164a0edcaf4b26161837 100644
--- a/lib/PublicInbox/LeiExternal.pm
+++ b/lib/PublicInbox/LeiExternal.pm
@@ -50,7 +50,7 @@ my %re_map = ( '*' => '[^/]*?', '?' => '[^/]',
 		'[' => '[', ']' => ']', ',' => ',' );
 
 sub glob2re {
-	my ($re) = @_;
+	my $re = $_[-1];
 	my $p = '';
 	my $in_bracket = 0;
 	my $qm = 0;
diff --git a/lib/PublicInbox/LeiLsSync.pm b/lib/PublicInbox/LeiLsSync.pm
new file mode 100644
index 0000000000000000000000000000000000000000..71f111a9e625bae7d1fb1a68c1cac968f44b8bf9
--- /dev/null
+++ b/lib/PublicInbox/LeiLsSync.pm
@@ -0,0 +1,29 @@
+# Copyright (C) 2021 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# front-end for the "lei ls-sync" sub-command
+package PublicInbox::LeiLsSync;
+use strict;
+use v5.10.1;
+use PublicInbox::LeiMailSync;
+
+sub lei_ls_sync {
+	my ($lei, $filter) = @_;
+	my $sto = $lei->_lei_store or return;
+	my $lms = $sto->search->lms or return;
+	my $opt = $lei->{opt};
+	my $re;
+	$re = defined($filter) ? qr/\Q$filter\E/ : qr/./ if $opt->{globoff};
+	$re //= $lei->glob2re($filter // '*');
+	my @f = $lms->folders;
+	@f = $opt->{'invert-match'} ? grep(!/$re/, @f) : grep(/$re/, @f);
+	if ($opt->{'local'} && !$opt->{remote}) {
+		@f = grep(!m!\A[a-z\+]+://!i, @f);
+	} elsif ($opt->{remote} && !$opt->{'local'}) {
+		@f = grep(m!\A[a-z\+]+://!i, @f);
+	}
+	my $ORS = $opt->{z} ? "\0" : "\n";
+	$lei->out(join($ORS, @f, ''));
+}
+
+1;
diff --git a/t/lei-import-imap.t b/t/lei-import-imap.t
index 4a3bd6d8541a2a923016a3edcd88aa9e024938d0..376a8b48673b9c84ed3bf10342a4c8af1cbca3f7 100644
--- a/t/lei-import-imap.t
+++ b/t/lei-import-imap.t
@@ -22,6 +22,8 @@ 	lei_ok('inspect', $url);
 	is_deeply(json_utf8->decode($lei_out), {}, 'no inspect stats, yet');
 
 	lei_ok('import', $url);
+	lei_ok 'ls-sync';
+	like($lei_out, qr!\A\Q$url\E;UIDVALIDITY=\d+\n\z!, 'ls-sync');
 
 	lei_ok('inspect', $url);
 	my $inspect = json_utf8->decode($lei_out);
diff --git a/t/lei-import-maildir.t b/t/lei-import-maildir.t
index 3e3d9188a2c5c4151fc0cebdbd9fd173fd354676..808e1a73b79bbffe410c7be5c957d56e1caaaf8c 100644
--- a/t/lei-import-maildir.t
+++ b/t/lei-import-maildir.t
@@ -40,6 +40,9 @@ 	is(ref(delete $inspect->{"lei/store"}), 'ARRAY', 'lei/store IDs');
 	is_deeply($inspect, { sync => { "maildir:$md" => [ 'x:2,S' ] } },
 		'maildir sync info as expected');
 
+	lei_ok qw(ls-sync);
+	is($lei_out, "maildir:$md\n", 'ls-sync as expected');
+
 	lei_ok(qw(import), $md, \'import Maildir again');
 	$imp_err = $lei_err;
 	lei_ok(qw(q -d none s:boolean), \'lei q w/o dedupe');