lib/PublicInbox/WwwText.pm | 29 ++++++++++++++++++++++++++++-
 t/extindex-psgi.t          | 12 ++++++++++++

diff --git a/lib/PublicInbox/WwwText.pm b/lib/PublicInbox/WwwText.pm
index db5060eaa460bf002c4377b93eb1b14c1cd5c7ba..eb5e3ac7b3edf49a0a049ab2503cd3e5c59798a0 100644
--- a/lib/PublicInbox/WwwText.pm
+++ b/lib/PublicInbox/WwwText.pm
@@ -214,10 +214,37 @@ 	}
 	1;
 }
 
+# n.b. this is a perfect candidate for memoization
+sub extindex_config ($$$) {
+	my ($ctx, $hdr, $txt) = @_;
+	my $ibx = $ctx->{ibx};
+	push @$hdr, 'Content-Disposition', 'inline; filename=extindex.config';
+	my $name = dq_escape($ibx->{name});
+	my $base_url = $ibx->base_url($ctx->{env});
+	$$txt .= <<EOS;
+; Example public-inbox config snippet for the external index (extindex) at:
+; $base_url
+; See public-inbox-config(5)manpage for more details:
+; https://public-inbox.org/public-inbox-config.html
+[extindex "$name"]
+	topdir = /path/to/extindex-topdir
+	url = https://example.com/$name/
+	url = http://example.onion/$name/
+EOS
+	for my $k (qw(infourl)) {
+		defined(my $v = $ibx->{$k}) or next;
+		$$txt .= "\t$k = $v\n";
+	}
+	# TODO: coderepo support for extindex
+	1;
+}
+
 sub _default_text ($$$$) {
 	my ($ctx, $key, $hdr, $txt) = @_;
 	return _colors_help($ctx, $txt) if $key eq 'color';
-	return inbox_config($ctx, $hdr, $txt) if $key eq 'config';
+	$key eq 'config' and return $ctx->{ibx}->can('cloneurl') ?
+			inbox_config($ctx, $hdr, $txt) :
+			extindex_config($ctx, $hdr, $txt);
 	return if $key ne 'help'; # TODO more keys?
 
 	my $ibx = $ctx->{ibx};
diff --git a/t/extindex-psgi.t b/t/extindex-psgi.t
index 6f62b5a035be0cd040a78876f8609116e4d5d4a7..b9acc9793292b6d3b7a7189853c01b75af186279 100644
--- a/t/extindex-psgi.t
+++ b/t/extindex-psgi.t
@@ -40,6 +40,18 @@ 	like($res->content, qr!http://usethis\.example\.com/!s,
 		'Host: header respected in Atom feed');
 	unlike($res->content, qr!http://bogus\.example\.com/!s,
 		'default URL ignored with different host header');
+
+	$res = $cb->(GET('/all/_/text/config/'));
+	is($res->code, 200, '/text/config HTML');
+	$res = $cb->(GET('/all/_/text/config/raw'));
+	is($res->code, 200, '/text/config raw');
+	my $f = "$tmpdir/extindex.config";
+	open my $fh, '>', $f or xbail $!;
+	print $fh $res->content or xbail $!;
+	close $fh or xbail $!;
+	my $cfg = PublicInbox::Config->git_config_dump($f);
+	is($?, 0, 'no errors from git-config parsing');
+	ok($cfg->{'extindex.all.topdir'}, 'extindex.topdir defined');
 };
 test_psgi(sub { $www->call(@_) }, $client);
 %$env = (%$env, TMPDIR => $tmpdir, PI_CONFIG => $pi_config);