[PATCH v3] checkpatch: add --json output mode

Sasha Levin
2026-04-25T20:04:34Z

Add a --json flag to checkpatch.pl that emits structured JSON output,
making results machine-parseable for CI systems, IDE integrations, and
AI-assisted code review tools.

The JSON output includes per-file totals (errors, warnings, checks,
lines) and an array of individual issues with structured fields for
level, type, message, file path, and line number.

A separate --json-pretty flag emits the same JSON in a pretty-printed
(indented, multi-line) form for human reading.

The --json (and --json-pretty) flags are mutually exclusive with
--terse and --emacs. Normal text output behaviour is completely
unchanged when --json is not specified.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
v3:
- Report the same line numbers text mode prints (matches --emacs
and --showfile). Fixes wrong locations on commit-message issues.
- Drop redundant defined() checks and `+ 0` coercions in the JSON
code; the values are already numeric and always defined.
- Add --json-pretty for indented output.
- Add parens around print() arguments.
- Consolidate the three empty-result early exits into one block.
- Return at the JSON branch instead of wrapping the rest of
process() in an else, so multi-file runs emit one document per
file and the indentation is no longer misleading.
v2: https://lore.kernel.org/all/20260408172435.1268067-1-sashal@kernel.org/
v1: https://lore.kernel.org/all/20260406170039.4034716-1-sashal@kernel.org/

Documentation/dev-tools/checkpatch.rst | 13 ++++
scripts/checkpatch.pl | 86 +++++++++++++++++++-------
2 files changed, 78 insertions(+), 21 deletions(-)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index dccede68698ca..8a7c7742b23fa 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -64,6 +64,19 @@ Available options:

Output only one line per report.

+ - --json
+
+ Output results as a JSON object. The object includes total error,
+ warning, and check counts, plus an array of individual issues with
+ structured fields for level, type, message, file, and line number.
+ Output is one compact JSON document per input file, suitable for CI
+ and scripted post-processing. Cannot be used with --terse or --emacs.
+
+ - --json-pretty
+
+ Like --json, but emit pretty-printed (indented, multi-line) JSON for
+ human reading.
+
- --showfile

Show the diffed file position instead of the input file position.
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0492d6afc9a1f..181bd10b046b7 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -14,6 +14,7 @@ use File::Basename;
use Cwd 'abs_path';
use Term::ANSIColor qw(:constants);
use Encode qw(decode encode);
+use JSON::PP;

my $P = $0;
my $D = dirname(abs_path($P));
@@ -33,6 +34,8 @@ my $chk_patch = 1;
my $tst_only;
my $emacs = 0;
my $terse = 0;
+my $json = 0;
+my $json_pretty = 0;
my $showfile = 0;
my $file = 0;
my $git = 0;
@@ -93,6 +96,8 @@ Options:
--patch treat FILE as patchfile (default)
--emacs emacs compile window format
--terse one line per report
+ --json output results as JSON
+ --json-pretty like --json, but pretty-printed
--showfile emit diffed file position, not input file position
-g, --git treat FILE as a single commit or git revision range
single git commit with:
@@ -320,6 +325,8 @@ GetOptions(
'patch!' => \$chk_patch,
'emacs!' => \$emacs,
'terse!' => \$terse,
+ 'json!' => \$json,
+ 'json-pretty!' => \$json_pretty,
'showfile!' => \$showfile,
'f|file!' => \$file,
'g|git!' => \$git,
@@ -380,6 +387,9 @@ help($help - 1) if ($help);
die "$P: --git cannot be used with --file or --fix\n" if ($git && ($file || $fix));
die "$P: --verbose cannot be used with --terse\n" if ($verbose && $terse);

+$json = 1 if ($json_pretty);
+die "$P: --json cannot be used with --terse or --emacs\n" if ($json && ($terse || $emacs));
+
if ($color =~ /^[01]$/) {
$color = !$color;
} elsif ($color =~ /^always$/i) {
@@ -1352,7 +1362,7 @@ for my $filename (@ARGV) {
}
close($FILE);

- if ($#ARGV > 0 && $quiet == 0) {
+ if (!$json && $#ARGV > 0 && $quiet == 0) {
print '-' x length($vname) . "\n";
print "$vname\n";
print '-' x length($vname) . "\n";
@@ -1373,7 +1383,7 @@ for my $filename (@ARGV) {
$file = $oldfile if ($is_git_file);
}

-if (!$quiet) {
+if (!$quiet && !$json) {
hash_show_words(\%use_type, "Used");
hash_show_words(\%ignore_type, "Ignored");

@@ -2396,6 +2406,19 @@ sub report {

push(our @report, $output);

+ if ($json) {
+ our ($realfile, $realline, $linenr);
+ my $line = ($file || $showfile) ? $realline : $linenr;
+ my %issue = (
+ level => $level,
+ type => $type,
+ message => $msg,
+ );
+ $issue{file} = $realfile if ($realfile ne '');
+ $issue{line} = $line if ($line);
+ push(our @json_issues, \%issue);
+ }
+
return 1;
}

@@ -2403,6 +2426,24 @@ sub report_dump {
our @report;
}

+sub json_print_result {
+ my ($filename, $total_errors, $total_warnings, $total_checks,
+ $total_lines, $issues, $used_types, $ignored_types) = @_;
+ my %result = (
+ filename => $filename,
+ total_errors => $total_errors,
+ total_warnings => $total_warnings,
+ total_checks => $total_checks,
+ total_lines => $total_lines,
+ issues => $issues,
+ );
+ $result{used_types} = $used_types if (defined $used_types);
+ $result{ignored_types} = $ignored_types if (defined $ignored_types);
+ my $json_encoder = JSON::PP->new->canonical->utf8;
+ $json_encoder->pretty if ($json_pretty);
+ print($json_encoder->encode(\%result), "\n");
+}
+
sub fixup_current_range {
my ($lineRef, $offset, $length) = @_;

@@ -2653,7 +2694,7 @@ sub is_userspace {
sub process {
my $filename = shift;

- my $linenr=0;
+ our $linenr=0;
my $prevline="";
my $prevrawline="";
my $stashline="";
@@ -2691,14 +2732,15 @@ sub process {
my $last_coalesced_string_linenr = -1;

our @report = ();
+ our @json_issues = ();
our $cnt_lines = 0;
our $cnt_error = 0;
our $cnt_warn = 0;
our $cnt_chk = 0;

# Trace the real file/line as we go.
- my $realfile = '';
- my $realline = 0;
+ our $realfile = '';
+ our $realline = 0;
my $realcnt = 0;
my $here = '';
my $context_function; #undef'd unless there's a known function
@@ -7806,21 +7848,14 @@ sub process {
}
}

- # If we have no input at all, then there is nothing to report on
- # so just keep quiet.
- if ($#rawlines == -1) {
- exit(0);
- }
-
- # In mailback mode only produce a report in the negative, for
- # things that appear to be patches.
- if ($mailback && ($clean == 1 || !$is_patch)) {
- exit(0);
- }
-
- # This is not a patch, and we are in 'no-patch' mode so
- # just keep quiet.
- if (!$chk_patch && !$is_patch) {
+ # Bail out early without producing a normal report when there is no
+ # input at all, when we are in mailback mode and either the patch is
+ # clean or the input does not appear to be a patch, or when the input
+ # is not a patch and we are in 'no-patch' mode.
+ if ($#rawlines == -1 ||
+ ($mailback && ($clean == 1 || !$is_patch)) ||
+ (!$chk_patch && !$is_patch)) {
+ json_print_result($filename, 0, 0, 0, 0, []) if ($json);
exit(0);
}

@@ -7868,7 +7903,16 @@ sub process {
}
}

- print report_dump();
+ if ($json) {
+ my @used = sort keys %use_type;
+ my @ignored = sort keys %ignore_type;
+ json_print_result($filename, $cnt_error, $cnt_warn,
+ $cnt_chk, $cnt_lines, \@json_issues,
+ \@used, \@ignored);
+ return $clean;
+ }
+
+ print(report_dump());
if ($summary && !($clean == 1 && $quiet == 1)) {
print "$filename " if ($summary_file);
print "total: $cnt_error errors, $cnt_warn warnings, " .
--
2.53.0