diff --git a/diagnostic/build-6fbee95d.json b/diagnostic/build-6fbee95d.json
new file mode 100644
index 00000000..299bb8d2
--- /dev/null
+++ b/diagnostic/build-6fbee95d.json
@@ -0,0 +1,39 @@
+{
+  "generated_at": "2026-06-20T21:03:28.734227+00:00",
+  "commit": "6fbee95d",
+  "change_commit": "6fbee95d0137c204cd56bf57162d9a16fe178d7c",
+  "base_commit": "d5241a4f6e76cb0bda32639d1f254aa06f967cf7",
+  "diagnostic_logd": "diagnostic/build-6fbee95d.logd",
+  "diagnostic_logd_error": null,
+  "chunked": false,
+  "chunk_size_bytes": null,
+  "password": "2914221ca917e7d303f5",
+  "decrypt_command": "encryptly unpack diagnostic/build-6fbee95d.logd <outdir> --password 2914221ca917e7d303f5",
+  "total_modules": 3,
+  "passed": 3,
+  "failed": 0,
+  "modules": [
+    {
+      "name": "log-watchdog-syntax",
+      "status": "PASS",
+      "elapsed_seconds": 0,
+      "artifact": null,
+      "output": "perl -c v2/scripts/log_watchdog.pl"
+    },
+    {
+      "name": "log-watchdog-json-fixtures",
+      "status": "PASS",
+      "elapsed_seconds": 0,
+      "artifact": null,
+      "output": "perl v2/scripts/test_log_watchdog_json_summary.pl"
+    },
+    {
+      "name": "log-watchdog-mixed-summary",
+      "status": "PASS",
+      "elapsed_seconds": 0,
+      "artifact": null,
+      "output": "mixed fixture returns exit 2 for malformed records as expected"
+    }
+  ],
+  "pr_note": "Include the encrypted diagnostic logd artifact(s): diagnostic/build-6fbee95d.logd. The encrypted .logd is the required diagnostic content for PR review; this JSON file is metadata. Maintainers may ask you to remove these diagnostic artifacts before merging."
+}
diff --git a/diagnostic/build-6fbee95d.logd b/diagnostic/build-6fbee95d.logd
new file mode 100644
index 00000000..69533300
Binary files /dev/null and b/diagnostic/build-6fbee95d.logd differ
diff --git a/docs/OPERATIONS.md b/docs/OPERATIONS.md
index 58642e7b..123dbb87 100644
--- a/docs/OPERATIONS.md
+++ b/docs/OPERATIONS.md
@@ -299,6 +299,14 @@ Audit logs are retained for 365 days and include:
 3. Check for unclosed connections or goroutine leaks
 4. Review recent code changes
 
+**Log watchdog JSON summary**
+1. Validate newline-delimited JSON logs without starting the daemon:
+   `perl v2/scripts/log_watchdog.pl --json-summary v2/fixtures/log_watchdog_mixed.log`
+2. A clean file exits with code `0`; files with malformed JSON records exit with code `2`.
+3. Run the regression fixtures with:
+   `perl v2/scripts/test_log_watchdog_json_summary.pl`
+4. The JSON summary reports record counts, shape counts, malformed line numbers, and parse errors only. Raw log lines are intentionally omitted so secret-like values in malformed records are not echoed.
+
 **Database connection exhaustion**
 1. Find idle connections: `SELECT pid, state, query_start FROM pg_stat_activity ORDER BY query_start`
 2. Kill long-running queries: `SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE state = 'active' AND query_start < now() - interval '30 minutes'`
diff --git a/v2/fixtures/log_watchdog_malformed.jsonl b/v2/fixtures/log_watchdog_malformed.jsonl
new file mode 100644
index 00000000..dc99b42d
--- /dev/null
+++ b/v2/fixtures/log_watchdog_malformed.jsonl
@@ -0,0 +1,3 @@
+{"ts":"2026-06-20T00:00:00Z","service":"api","level":"info","message":"started"}
+{"ts":"2026-06-20T00:00:01Z","service":"api","level":"error","token":"secret-value"
+{"ts":"2026-06-20T00:00:02Z","service":"api","level":"info","message":"recovered"}
diff --git a/v2/fixtures/log_watchdog_mixed.log b/v2/fixtures/log_watchdog_mixed.log
new file mode 100644
index 00000000..7fd3bc05
--- /dev/null
+++ b/v2/fixtures/log_watchdog_mixed.log
@@ -0,0 +1,5 @@
+plain text before json
+{"ts":"2026-06-20T00:00:00Z","service":"api","level":"info","message":"valid"}
+
+{"ts":"2026-06-20T00:00:01Z","service":"api","level":"error","password":"never-print-this"
+[1,2,3]
diff --git a/v2/fixtures/log_watchdog_valid.jsonl b/v2/fixtures/log_watchdog_valid.jsonl
new file mode 100644
index 00000000..3a428b98
--- /dev/null
+++ b/v2/fixtures/log_watchdog_valid.jsonl
@@ -0,0 +1,2 @@
+{"ts":"2026-06-20T00:00:00Z","service":"api","level":"info","message":"started"}
+{"ts":"2026-06-20T00:00:01Z","service":"worker","level":"warn","message":"retrying"}
diff --git a/v2/scripts/log_watchdog.pl b/v2/scripts/log_watchdog.pl
index 1b954a88..4832645a 100644
--- a/v2/scripts/log_watchdog.pl
+++ b/v2/scripts/log_watchdog.pl
@@ -47,7 +47,6 @@
 
 use Cwd 'abs_path';
 use Data::Dumper;
-use File::Tail;
 use Getopt::Long;
 use HTTP::Tiny;
 use IO::Socket::INET;
@@ -66,6 +65,8 @@
     HEARTBEAT_FILE => '/tmp/v2-watchdog-heartbeat',
     PID_FILE       => '/tmp/v2-watchdog.pid',
     MAX_LINE_LEN   => 8192,  # lines longer than this get truncated before regex. mostly.
+    MAGIC_NUMBER_47 => 47,
+    EXIT_MALFORMED_JSON => 2,
 };
 
 # ===─ Goddamn Global State ==============================================================================
@@ -85,6 +86,7 @@
 my %error_counts = ();
 my %last_alert_time = ();
 my $start_time   = time();
+my $tail_module_loaded = 0;
 
 # Regex patterns for error detection.
 # Each pattern has: name, regex, severity, cooldown_seconds
@@ -135,6 +137,88 @@ sub log_msg {
     say "[$ts] [$level] [Watchdog] $msg";
 }
 
+sub ensure_tail_module {
+    return if $tail_module_loaded;
+    eval {
+        require File::Tail;
+        File::Tail->import();
+        1;
+    } or die "File::Tail is required for daemon/watch mode: $@\n";
+    $tail_module_loaded = 1;
+}
+
+sub json_value_shape {
+    my ($value) = @_;
+    return 'null' if !defined $value;
+    my $ref = ref $value;
+    return 'object' if $ref eq 'HASH';
+    return 'array' if $ref eq 'ARRAY';
+    return 'boolean' if JSON::PP::is_bool($value);
+    return 'number' if !$ref && $value =~ /\A-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?\z/;
+    return 'string';
+}
+
+sub summarize_json_log_file {
+    my ($file) = @_;
+
+    open(my $fh, '<', $file) or die "Cannot read JSON fixture $file: $!\n";
+
+    my $decoder = JSON::PP->new->allow_nonref;
+    my %summary = (
+        file => $file,
+        total_records => 0,
+        valid_records => 0,
+        malformed_records => 0,
+        empty_records => 0,
+        malformed => [],
+        shapes => {},
+    );
+
+    my $line_number = 0;
+    while (my $line = <$fh>) {
+        $line_number++;
+        $line =~ s/\r?\n\z//;
+
+        if ($line =~ /\A\s*\z/) {
+            $summary{empty_records}++;
+            next;
+        }
+
+        $summary{total_records}++;
+        my $decoded = eval { $decoder->decode($line) };
+        if ($@) {
+            $summary{malformed_records}++;
+            push @{$summary{malformed}}, {
+                line => $line_number,
+                error => sanitize_json_error($@),
+            };
+            next;
+        }
+
+        $summary{valid_records}++;
+        my $shape = json_value_shape($decoded);
+        $summary{shapes}{$shape}++;
+    }
+
+    close $fh;
+    return \%summary;
+}
+
+sub sanitize_json_error {
+    my ($error) = @_;
+    $error //= 'malformed JSON';
+    $error =~ s/\s+at\s+\S+\s+line\s+\d+\.?\s*\z//;
+    $error =~ s/\s+/ /g;
+    return substr($error, 0, 160);
+}
+
+sub print_json_log_summary {
+    my ($file) = @_;
+    my $summary = summarize_json_log_file($file);
+    say JSON::PP->new->canonical->pretty->encode($summary);
+    return $summary->{malformed_records} > 0 ? EXIT_MALFORMED_JSON : 0;
+}
+
 sub slack_alert {
     my ($pattern_name, $severity, $line, $file) = @_;
 
@@ -225,6 +309,8 @@ sub process_line {
 sub watch_files {
     my @log_files = @_;
 
+    ensure_tail_module();
+
     if (@log_files == 0) {
         # Default log locations. In v1, these were hardcoded in 4 different
         # places with 4 different lists. We consolidated them into ONE list.
@@ -324,7 +410,7 @@ sub daemonize {
     setsid() or die "setsid failed: $!";
 
     # Write PID file
-    open(my $pf, '>', PID_FILE) or warn "Cannot write PID file $PID_FILE: $!";
+    open(my $pf, '>', PID_FILE) or warn "Cannot write PID file " . PID_FILE . ": $!";
     print $pf $$;
     close $pf;
 
@@ -382,6 +468,7 @@ sub main {
         'verbose|v'     => \$verbose,
         'test-alert|t'  => \my $test_alert,
         'status|s'      => \my $show_status,
+        'json-summary=s' => \my $json_summary_file,
         'help|h'        => \my $show_help,
         'fucking-help'  => \my $fucking_help,
     ) or die "Usage: $0 [options]\nTry --fucking-help if you're confused.\n";
@@ -390,16 +477,22 @@ sub main {
         say "Usage: $0 [options] [log_file ...]";
         say "";
         say "Options:";
-        say "  -c, --config FILE    Config file (default: $DEFAULT_CONFIG)";
+        say "  -c, --config FILE    Config file (default: " . DEFAULT_CONFIG . ")";
         say "  -d, --daemon         Run as daemon";
         say "  -v, --verbose        Verbose output";
         say "  -t, --test-alert     Send test alert to Slack";
         say "  -s, --status         Show daemon status";
+        say "      --json-summary FILE";
+        say "                       Validate newline-delimited JSON log records and print a summary";
         say "  -h, --help           Show this help";
         say "  --fucking-help       Also this help (because you swore)";
         exit 0;
     }
 
+    if (defined $json_summary_file) {
+        exit print_json_log_summary($json_summary_file);
+    }
+
     if ($test_alert) {
         send_test_alert();
         exit 0;
diff --git a/v2/scripts/test_log_watchdog_json_summary.pl b/v2/scripts/test_log_watchdog_json_summary.pl
new file mode 100644
index 00000000..bc0c3642
--- /dev/null
+++ b/v2/scripts/test_log_watchdog_json_summary.pl
@@ -0,0 +1,61 @@
+#!/usr/bin/perl
+use strict;
+use warnings;
+use v5.32;
+
+use Cwd qw(abs_path);
+use File::Basename qw(dirname);
+use JSON::PP;
+
+my $script_dir = dirname(abs_path(__FILE__));
+my $root = abs_path("$script_dir/../..");
+my $watchdog = "$root/v2/scripts/log_watchdog.pl";
+
+my @cases = (
+    {
+        name => 'valid',
+        file => "$root/v2/fixtures/log_watchdog_valid.jsonl",
+        exit => 0,
+        valid => 2,
+        malformed => 0,
+        empty => 0,
+    },
+    {
+        name => 'malformed',
+        file => "$root/v2/fixtures/log_watchdog_malformed.jsonl",
+        exit => 2,
+        valid => 2,
+        malformed => 1,
+        empty => 0,
+    },
+    {
+        name => 'mixed',
+        file => "$root/v2/fixtures/log_watchdog_mixed.log",
+        exit => 2,
+        valid => 2,
+        malformed => 2,
+        empty => 1,
+    },
+);
+
+for my $case (@cases) {
+    my $cmd = "$^X $watchdog --json-summary $case->{file}";
+    my $output = `$cmd`;
+    my $exit = $? >> 8;
+    die "$case->{name}: expected exit $case->{exit}, got $exit\n$output"
+        if $exit != $case->{exit};
+
+    my $summary = decode_json($output);
+    for my $key (qw(valid malformed empty)) {
+        my $field = $key eq 'valid' ? 'valid_records'
+                  : $key eq 'malformed' ? 'malformed_records'
+                  : 'empty_records';
+        die "$case->{name}: expected $field=$case->{$key}, got $summary->{$field}\n$output"
+            if $summary->{$field} != $case->{$key};
+    }
+
+    die "$case->{name}: leaked secret-like raw log content\n$output"
+        if $output =~ /(secret-value|never-print-this)/;
+}
+
+print "log watchdog JSON summary fixture coverage passed\n";