diff --git a/.perlcriticrc b/.perlcriticrc
index ddddcada..9d756697 100644
--- a/.perlcriticrc
+++ b/.perlcriticrc
@@ -1,4 +1,4 @@
 theme = community
 
 # 5 is the least complainy, 1 is the most complainy
-severity = 5
+severity = 4
diff --git a/flake.nix b/flake.nix
index 85b226de..1982e8b9 100644
--- a/flake.nix
+++ b/flake.nix
@@ -454,14 +454,14 @@
                 DigestSHA1
                 EmailMIME
                 EmailSender
-                FileSlurp
+                FileSlurper
                 FileWhich
                 final.nix.perl-bindings
                 git
                 IOCompress
                 IPCRun
                 JSON
-                JSONAny
+                JSONMaybeXS
                 JSONXS
                 LWP
                 LWPProtocolHttps
diff --git a/src/Makefile.PL b/src/Makefile.PL
index 36b3e992..9b04da7f 100644
--- a/src/Makefile.PL
+++ b/src/Makefile.PL
@@ -1,5 +1,7 @@
 # IMPORTANT: if you delete this file your app will not work as
 # expected.  you have been warned
+use strict;
+use warnings;
 use inc::Module::Install;
 
 name 'Hydra';
diff --git a/src/lib/Hydra/Config.pm b/src/lib/Hydra/Config.pm
index a681f1c0..bb991822 100644
--- a/src/lib/Hydra/Config.pm
+++ b/src/lib/Hydra/Config.pm
@@ -1,5 +1,8 @@
 package Hydra::Config;
 
+use strict;
+use warnings;
+
 our %configGeneralOpts = (-UseApacheInclude => 1, -IncludeAgain => 1, -IncludeRelative => 1);
 
 1;
diff --git a/src/lib/Hydra/Controller/API.pm b/src/lib/Hydra/Controller/API.pm
index b2167b5b..474a0021 100644
--- a/src/lib/Hydra/Controller/API.pm
+++ b/src/lib/Hydra/Controller/API.pm
@@ -8,11 +8,10 @@ use Hydra::Helper::Nix;
 use Hydra::Helper::CatalystUtils;
 use Hydra::Controller::Project;
 use JSON;
-use JSON::Any;
+use JSON::MaybeXS;
 use DateTime;
 use Digest::SHA qw(sha256_hex);
 use Text::Diff;
-use File::Slurp;
 use IPC::Run qw(run);
 
 
@@ -67,7 +66,7 @@ sub latestbuilds : Chained('api') PathPart('latestbuilds') Args(0) {
     push @list, buildToHash($_) foreach @latest;
 
     $c->stash->{'plain'} = {
-        data => scalar (JSON::Any->objToJson(\@list))
+        data => scalar (encode_json(\@list))
     };
     $c->forward('Hydra::View::Plain');
 }
@@ -108,7 +107,7 @@ sub jobsets : Chained('api') PathPart('jobsets') Args(0) {
     push @list, jobsetToHash($_) foreach @jobsets;
 
     $c->stash->{'plain'} = {
-        data => scalar (JSON::Any->objToJson(\@list))
+        data => scalar (encode_json(\@list))
     };
     $c->forward('Hydra::View::Plain');
 }
@@ -126,7 +125,7 @@ sub queue : Chained('api') PathPart('queue') Args(0) {
     push @list, buildToHash($_) foreach @builds;
 
     $c->stash->{'plain'} = {
-        data => scalar (JSON::Any->objToJson(\@list))
+        data => scalar (encode_json(\@list))
     };
     $c->forward('Hydra::View::Plain');
 }
@@ -170,7 +169,7 @@ sub nrbuilds : Chained('api') PathPart('nrbuilds') Args(0) {
     @arr = reverse(@arr);
 
     $c->stash->{'plain'} = {
-        data => scalar (JSON::Any->objToJson(\@arr))
+        data => scalar (encode_json(\@arr))
     };
     $c->forward('Hydra::View::Plain');
 }
diff --git a/src/lib/Hydra/Controller/Build.pm b/src/lib/Hydra/Controller/Build.pm
index 765dcbd7..27535f2e 100644
--- a/src/lib/Hydra/Controller/Build.pm
+++ b/src/lib/Hydra/Controller/Build.pm
@@ -8,7 +8,6 @@ use Hydra::Helper::Nix;
 use Hydra::Helper::CatalystUtils;
 use File::Basename;
 use File::stat;
-use File::Slurp;
 use Data::Dump qw(dump);
 use Nix::Store;
 use Nix::Config;
diff --git a/src/lib/Hydra/Controller/Job.pm b/src/lib/Hydra/Controller/Job.pm
index becd364b..378887ea 100644
--- a/src/lib/Hydra/Controller/Job.pm
+++ b/src/lib/Hydra/Controller/Job.pm
@@ -6,6 +6,7 @@ use warnings;
 use base 'Hydra::Base::Controller::ListBuilds';
 use Hydra::Helper::Nix;
 use Hydra::Helper::CatalystUtils;
+use JSON::MaybeXS;
 use Net::Prometheus;
 
 sub job : Chained('/') PathPart('job') CaptureArgs(3) {
@@ -50,7 +51,7 @@ sub shield :Chained('job') PathPart('shield') Args(0) {
 
     $c->response->content_type('application/json');
     $c->stash->{'plain'} = {
-        data => scalar (JSON::Any->objToJson(
+        data => scalar (encode_json(
             {
                 schemaVersion => 1,
                 label => "hydra build",
diff --git a/src/lib/Hydra/Controller/User.pm b/src/lib/Hydra/Controller/User.pm
index 852dd16d..f22075b9 100644
--- a/src/lib/Hydra/Controller/User.pm
+++ b/src/lib/Hydra/Controller/User.pm
@@ -4,7 +4,7 @@ use utf8;
 use strict;
 use warnings;
 use base 'Hydra::Base::Controller::REST';
-use File::Slurp;
+use File::Slurper qw(read_text);
 use Crypt::RandPasswd;
 use Digest::SHA1 qw(sha1_hex);
 use Hydra::Helper::Nix;
@@ -165,7 +165,7 @@ sub github_login :Path('/github-login') Args(0) {
     my $client_id = $c->config->{github_client_id} or die "github_client_id not configured.";
     my $client_secret = $c->config->{github_client_secret} // do {
         my $client_secret_file = $c->config->{github_client_secret_file} or die "github_client_secret nor github_client_secret_file is configured.";
-        my $client_secret = read_file($client_secret_file);
+        my $client_secret = read_text($client_secret_file);
         $client_secret =~ s/\s+//;
         $client_secret;
     };
diff --git a/src/lib/Hydra/Event.pm b/src/lib/Hydra/Event.pm
index cd8bdde2..e3954308 100644
--- a/src/lib/Hydra/Event.pm
+++ b/src/lib/Hydra/Event.pm
@@ -1,6 +1,7 @@
 package Hydra::Event;
 
 use strict;
+use warnings;
 use Hydra::Event::BuildFinished;
 use Hydra::Event::BuildStarted;
 use Hydra::Event::StepFinished;
diff --git a/src/lib/Hydra/Helper/AddBuilds.pm b/src/lib/Hydra/Helper/AddBuilds.pm
index d928943a..bf520321 100644
--- a/src/lib/Hydra/Helper/AddBuilds.pm
+++ b/src/lib/Hydra/Helper/AddBuilds.pm
@@ -1,6 +1,7 @@
 package Hydra::Helper::AddBuilds;
 
 use strict;
+use warnings;
 use utf8;
 use Encode;
 use JSON;
@@ -14,7 +15,6 @@ use File::stat;
 use File::Path;
 use File::Temp;
 use File::Spec;
-use File::Slurp;
 use Hydra::Helper::CatalystUtils;
 
 our @ISA = qw(Exporter);
diff --git a/src/lib/Hydra/Helper/CatalystUtils.pm b/src/lib/Hydra/Helper/CatalystUtils.pm
index cd3a0fd7..0b48e455 100644
--- a/src/lib/Hydra/Helper/CatalystUtils.pm
+++ b/src/lib/Hydra/Helper/CatalystUtils.pm
@@ -2,6 +2,7 @@ package Hydra::Helper::CatalystUtils;
 
 use utf8;
 use strict;
+use warnings;
 use Exporter;
 use Readonly;
 use Nix::Store;
diff --git a/src/lib/Hydra/Helper/Email.pm b/src/lib/Hydra/Helper/Email.pm
index 44366f43..b66f427b 100644
--- a/src/lib/Hydra/Helper/Email.pm
+++ b/src/lib/Hydra/Helper/Email.pm
@@ -1,10 +1,10 @@
 package Hydra::Helper::Email;
 
 use strict;
+use warnings;
 use Email::MIME;
 use Email::Sender::Simple qw(sendmail);
 use Exporter 'import';
-use File::Slurp;
 use Hydra::Helper::Nix;
 use Sys::Hostname::Long;
 
diff --git a/src/lib/Hydra/Helper/Escape.pm b/src/lib/Hydra/Helper/Escape.pm
index 3037951f..8458f885 100644
--- a/src/lib/Hydra/Helper/Escape.pm
+++ b/src/lib/Hydra/Helper/Escape.pm
@@ -1,6 +1,7 @@
 package Hydra::Helper::Escape;
 
 use strict;
+use warnings;
 use base qw(Exporter);
 use Hydra::Helper::AttributeSet;
 
diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index bd294b73..e76ac18b 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -1,6 +1,7 @@
 package Hydra::Helper::Nix;
 
 use strict;
+use warnings;
 use Exporter;
 use File::Path;
 use File::Basename;
@@ -65,8 +66,8 @@ sub getStatsdConfig {
     my %statsd = defined $cfg ? ref $cfg eq "HASH" ? %$cfg : ($cfg) : ();
 
     return {
-        "host" => %statsd{'host'}  // 'localhost',
-        "port" => %statsd{'port'}  // 8125,
+        "host" => $statsd{'host'}  // 'localhost',
+        "port" => $statsd{'port'}  // 8125,
     }
 }
 
@@ -83,20 +84,20 @@ sub getHydraNotifyPrometheusConfig {
         return undef;
     }
 
-    my $cfg = $cfg->{prometheus};
-    if (!defined($cfg)) {
+    my $promcfg = $cfg->{prometheus};
+    if (!defined($promcfg)) {
         return undef;
     }
 
-    if (ref $cfg ne "HASH") {
+    if (ref $promcfg ne "HASH") {
         print STDERR "Error reading Hydra's configuration file: hydra_notify.prometheus should be a block.\n";
         return undef;
     }
 
-    if (defined($cfg->{"listen_address"}) && defined($cfg->{"port"})) {
+    if (defined($promcfg->{"listen_address"}) && defined($promcfg->{"port"})) {
         return {
-            "listen_address" => $cfg->{'listen_address'},
-            "port" => $cfg->{'port'},
+            "listen_address" => $promcfg->{'listen_address'},
+            "port" => $promcfg->{'port'},
         };
     } else {
         print STDERR "Error reading Hydra's configuration file: hydra_notify.prometheus should include listen_address and port.\n";
@@ -140,8 +141,8 @@ sub registerRoot {
     my ($path) = @_;
     my $link = gcRootFor $path;
     return if -e $link;
-    open ROOT, ">$link" or die "cannot create GC root `$link' to `$path'";
-    close ROOT;
+    open my $root, ">$link" or die "cannot create GC root `$link' to `$path'";
+    close $root;
 }
 
 
@@ -305,7 +306,8 @@ sub getEvals {
             { order_by => "id DESC", rows => 1 });
 
         my $curInfo = getEvalInfo($cache, $curEval);
-        my $prevInfo = getEvalInfo($cache, $prevEval) if defined $prevEval;
+        my $prevInfo;
+        $prevInfo = getEvalInfo($cache, $prevEval) if defined $prevEval;
 
         # Compute what inputs changed between each eval.
         my @changedInputs;
@@ -340,12 +342,12 @@ sub getMachines {
 
     for my $machinesFile (@machinesFiles) {
         next unless -e $machinesFile;
-        open CONF, "<$machinesFile" or die;
-        while (<CONF>) {
+        open my $conf, "<$machinesFile" or die;
+        while (my $line = <$conf>) {
             chomp;
             s/\#.*$//g;
             next if /^\s*$/;
-            my @tokens = split /\s/, $_;
+            my @tokens = split /\s/, $line;
             my @supportedFeatures = split(/,/, $tokens[5] || "");
             my @mandatoryFeatures = split(/,/, $tokens[6] || "");
             $machines{$tokens[0]} =
@@ -357,7 +359,7 @@ sub getMachines {
                 , mandatoryFeatures => [ @mandatoryFeatures ]
                 };
         }
-        close CONF;
+        close $conf;
     }
 
     return \%machines;
diff --git a/src/lib/Hydra/Model/DB.pm b/src/lib/Hydra/Model/DB.pm
index 7514302e..d3a401c3 100644
--- a/src/lib/Hydra/Model/DB.pm
+++ b/src/lib/Hydra/Model/DB.pm
@@ -1,6 +1,7 @@
 package Hydra::Model::DB;
 
 use strict;
+use warnings;
 use base 'Catalyst::Model::DBIC::Schema';
 
 sub getHydraPath {
diff --git a/src/lib/Hydra/Plugin.pm b/src/lib/Hydra/Plugin.pm
index 119d2738..a3526427 100644
--- a/src/lib/Hydra/Plugin.pm
+++ b/src/lib/Hydra/Plugin.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin;
 
 use strict;
+use warnings;
 use Module::Pluggable
     search_path => "Hydra::Plugin",
     instantiate => 'new';
diff --git a/src/lib/Hydra/Plugin/BazaarInput.pm b/src/lib/Hydra/Plugin/BazaarInput.pm
index db26172f..458f5141 100644
--- a/src/lib/Hydra/Plugin/BazaarInput.pm
+++ b/src/lib/Hydra/Plugin/BazaarInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::BazaarInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Digest::SHA qw(sha256_hex);
 use File::Path;
diff --git a/src/lib/Hydra/Plugin/BitBucketPulls.pm b/src/lib/Hydra/Plugin/BitBucketPulls.pm
index 1a50f6ec..5371d5f0 100644
--- a/src/lib/Hydra/Plugin/BitBucketPulls.pm
+++ b/src/lib/Hydra/Plugin/BitBucketPulls.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::BitBucketPulls;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/BitBucketStatus.pm b/src/lib/Hydra/Plugin/BitBucketStatus.pm
index 097bed00..72ed3b6b 100644
--- a/src/lib/Hydra/Plugin/BitBucketStatus.pm
+++ b/src/lib/Hydra/Plugin/BitBucketStatus.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::BitBucketStatus;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use JSON;
diff --git a/src/lib/Hydra/Plugin/CircleCINotification.pm b/src/lib/Hydra/Plugin/CircleCINotification.pm
index 398fe066..a2eb26a4 100644
--- a/src/lib/Hydra/Plugin/CircleCINotification.pm
+++ b/src/lib/Hydra/Plugin/CircleCINotification.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::CircleCINotification;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/CompressLog.pm b/src/lib/Hydra/Plugin/CompressLog.pm
index bf8d4327..10e8f6cc 100644
--- a/src/lib/Hydra/Plugin/CompressLog.pm
+++ b/src/lib/Hydra/Plugin/CompressLog.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::CompressLog;
 
 use strict;
+use warnings;
 use utf8;
 use parent 'Hydra::Plugin';
 use Hydra::Helper::CatalystUtils;
diff --git a/src/lib/Hydra/Plugin/CoverityScan.pm b/src/lib/Hydra/Plugin/CoverityScan.pm
index f395100f..c7b39d02 100644
--- a/src/lib/Hydra/Plugin/CoverityScan.pm
+++ b/src/lib/Hydra/Plugin/CoverityScan.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::CoverityScan;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use File::Basename;
 use LWP::UserAgent;
@@ -51,12 +52,12 @@ sub buildFinished {
     my $tarballs  = "$storePath/tarballs";
     my $covTarball;
 
-    opendir TARBALLS, $tarballs or die;
-    while (readdir TARBALLS) {
-        next unless $_ =~ /.*-coverity-int\.(tgz|lzma|xz|bz2|zip)$/;
-        $covTarball = "$tarballs/$_"; last;
+    opendir my $tarballs_handle, $tarballs or die;
+    while (my $file = readdir $tarballshandle) {
+        next unless $file =~ /.*-coverity-int\.(tgz|lzma|xz|bz2|zip)$/;
+        $covTarball = "$tarballs/$file"; last;
     }
-    closedir TARBALLS;
+    closedir $tarballs_handle;
 
     unless (defined $covTarball) {
         print STDERR "CoverityScan.pm: Coverity tarball not found in $tarballs; skipping upload...\n";
@@ -81,7 +82,8 @@ sub buildFinished {
     my $versionRE = "(?:[A-Za-z0-9\.\-]+)";
 
     my $shortName = basename($covTarball);
-    my $version = $2 if $shortName =~ /^($pkgNameRE)-($versionRE)-coverity-int.*$/;
+    my $version;
+    $version = $2 if $shortName =~ /^($pkgNameRE)-($versionRE)-coverity-int.*$/;
 
     die "CoverityScan.pm: Couldn't parse build version for upload! ($shortName)"
         unless defined $version;
diff --git a/src/lib/Hydra/Plugin/DarcsInput.pm b/src/lib/Hydra/Plugin/DarcsInput.pm
index 0091819a..42f6a9a4 100644
--- a/src/lib/Hydra/Plugin/DarcsInput.pm
+++ b/src/lib/Hydra/Plugin/DarcsInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::DarcsInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Digest::SHA qw(sha256_hex);
 use File::Path;
diff --git a/src/lib/Hydra/Plugin/DeclarativeJobsets.pm b/src/lib/Hydra/Plugin/DeclarativeJobsets.pm
index 2b6771b5..f59fa858 100644
--- a/src/lib/Hydra/Plugin/DeclarativeJobsets.pm
+++ b/src/lib/Hydra/Plugin/DeclarativeJobsets.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::DeclarativeJobsets;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Hydra::Helper::AddBuilds;
 
diff --git a/src/lib/Hydra/Plugin/EmailNotification.pm b/src/lib/Hydra/Plugin/EmailNotification.pm
index 4e6c7809..721365e1 100644
--- a/src/lib/Hydra/Plugin/EmailNotification.pm
+++ b/src/lib/Hydra/Plugin/EmailNotification.pm
@@ -2,6 +2,7 @@ package Hydra::Plugin::EmailNotification;
 
 use utf8;
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use POSIX qw(strftime);
 use Template;
diff --git a/src/lib/Hydra/Plugin/GitInput.pm b/src/lib/Hydra/Plugin/GitInput.pm
index 848c0dee..cd8d23e2 100644
--- a/src/lib/Hydra/Plugin/GitInput.pm
+++ b/src/lib/Hydra/Plugin/GitInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GitInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Digest::SHA qw(sha256_hex);
 use File::Path;
diff --git a/src/lib/Hydra/Plugin/GiteaStatus.pm b/src/lib/Hydra/Plugin/GiteaStatus.pm
index 75796053..567dfd09 100644
--- a/src/lib/Hydra/Plugin/GiteaStatus.pm
+++ b/src/lib/Hydra/Plugin/GiteaStatus.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GiteaStatus;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 
 use HTTP::Request;
diff --git a/src/lib/Hydra/Plugin/GithubPulls.pm b/src/lib/Hydra/Plugin/GithubPulls.pm
index 6a3cc951..fb497c76 100644
--- a/src/lib/Hydra/Plugin/GithubPulls.pm
+++ b/src/lib/Hydra/Plugin/GithubPulls.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GithubPulls;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/GithubRefs.pm b/src/lib/Hydra/Plugin/GithubRefs.pm
index 408159dd..1de2672d 100644
--- a/src/lib/Hydra/Plugin/GithubRefs.pm
+++ b/src/lib/Hydra/Plugin/GithubRefs.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GithubRefs;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/GithubStatus.pm b/src/lib/Hydra/Plugin/GithubStatus.pm
index e3dfc533..cda7426a 100644
--- a/src/lib/Hydra/Plugin/GithubStatus.pm
+++ b/src/lib/Hydra/Plugin/GithubStatus.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GithubStatus;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use JSON;
diff --git a/src/lib/Hydra/Plugin/GitlabPulls.pm b/src/lib/Hydra/Plugin/GitlabPulls.pm
index b44a1a98..3249ecf8 100644
--- a/src/lib/Hydra/Plugin/GitlabPulls.pm
+++ b/src/lib/Hydra/Plugin/GitlabPulls.pm
@@ -15,6 +15,7 @@
 package Hydra::Plugin::GitlabPulls;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/GitlabStatus.pm b/src/lib/Hydra/Plugin/GitlabStatus.pm
index 483d99bd..d19877ed 100644
--- a/src/lib/Hydra/Plugin/GitlabStatus.pm
+++ b/src/lib/Hydra/Plugin/GitlabStatus.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::GitlabStatus;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use JSON;
diff --git a/src/lib/Hydra/Plugin/HipChatNotification.pm b/src/lib/Hydra/Plugin/HipChatNotification.pm
index 9a7385c4..415cfafb 100644
--- a/src/lib/Hydra/Plugin/HipChatNotification.pm
+++ b/src/lib/Hydra/Plugin/HipChatNotification.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::HipChatNotification;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use LWP::UserAgent;
 use Hydra::Helper::CatalystUtils;
diff --git a/src/lib/Hydra/Plugin/InfluxDBNotification.pm b/src/lib/Hydra/Plugin/InfluxDBNotification.pm
index 21a3fa31..62200cc9 100644
--- a/src/lib/Hydra/Plugin/InfluxDBNotification.pm
+++ b/src/lib/Hydra/Plugin/InfluxDBNotification.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::InfluxDBNotification;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/MercurialInput.pm b/src/lib/Hydra/Plugin/MercurialInput.pm
index 8a9b4b43..3aaa0ba3 100644
--- a/src/lib/Hydra/Plugin/MercurialInput.pm
+++ b/src/lib/Hydra/Plugin/MercurialInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::MercurialInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Digest::SHA qw(sha256_hex);
 use File::Path;
diff --git a/src/lib/Hydra/Plugin/PathInput.pm b/src/lib/Hydra/Plugin/PathInput.pm
index d5c490f0..e7d98da2 100644
--- a/src/lib/Hydra/Plugin/PathInput.pm
+++ b/src/lib/Hydra/Plugin/PathInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::PathInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use POSIX qw(strftime);
 use Hydra::Helper::Nix;
diff --git a/src/lib/Hydra/Plugin/RunCommand.pm b/src/lib/Hydra/Plugin/RunCommand.pm
index 7cfb63c5..33295e50 100644
--- a/src/lib/Hydra/Plugin/RunCommand.pm
+++ b/src/lib/Hydra/Plugin/RunCommand.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::RunCommand;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use experimental 'smartmatch';
 use JSON;
diff --git a/src/lib/Hydra/Plugin/S3Backup.pm b/src/lib/Hydra/Plugin/S3Backup.pm
index 346cf239..bdd23b2f 100644
--- a/src/lib/Hydra/Plugin/S3Backup.pm
+++ b/src/lib/Hydra/Plugin/S3Backup.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::S3Backup;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use File::Temp;
 use File::Basename;
diff --git a/src/lib/Hydra/Plugin/SlackNotification.pm b/src/lib/Hydra/Plugin/SlackNotification.pm
index 387f92c4..5320dd7b 100644
--- a/src/lib/Hydra/Plugin/SlackNotification.pm
+++ b/src/lib/Hydra/Plugin/SlackNotification.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::SlackNotification;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use HTTP::Request;
 use LWP::UserAgent;
diff --git a/src/lib/Hydra/Plugin/SoTest.pm b/src/lib/Hydra/Plugin/SoTest.pm
index aed7a1b8..5b45f153 100644
--- a/src/lib/Hydra/Plugin/SoTest.pm
+++ b/src/lib/Hydra/Plugin/SoTest.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::SoTest;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Hydra::Helper::CatalystUtils;
 use HTTP::Request;
@@ -101,8 +102,8 @@ sub buildFinished {
     open( $authfile, "<", $sotest->{authfile} )
       or die "Cannot open Sotest authfile \${\$sotest->{authfile}}";
 
-    while (<$authfile>) {
-        if ( $_ =~ /(.+):(.+)/m ) {
+    while (my $line = <$authfile>) {
+        if ( $line =~ /(.+):(.+)/m ) {
             $sotest_username = $1;
             $sotest_password = $2;
         }
diff --git a/src/lib/Hydra/Plugin/SubversionInput.pm b/src/lib/Hydra/Plugin/SubversionInput.pm
index a8183e2c..7879364e 100644
--- a/src/lib/Hydra/Plugin/SubversionInput.pm
+++ b/src/lib/Hydra/Plugin/SubversionInput.pm
@@ -1,6 +1,7 @@
 package Hydra::Plugin::SubversionInput;
 
 use strict;
+use warnings;
 use parent 'Hydra::Plugin';
 use Digest::SHA qw(sha256_hex);
 use Hydra::Helper::Nix;
diff --git a/src/lib/Hydra/View/JSON.pm b/src/lib/Hydra/View/JSON.pm
index f2ab1fc8..d8924ac3 100644
--- a/src/lib/Hydra/View/JSON.pm
+++ b/src/lib/Hydra/View/JSON.pm
@@ -1,3 +1,5 @@
 package Hydra::View::JSON;
+use strict;
+use warnings;
 use base qw(Catalyst::View::JSON);
 1;
diff --git a/src/lib/Hydra/View/NARInfo.pm b/src/lib/Hydra/View/NARInfo.pm
index 460bd706..44db78b1 100644
--- a/src/lib/Hydra/View/NARInfo.pm
+++ b/src/lib/Hydra/View/NARInfo.pm
@@ -1,5 +1,7 @@
 package Hydra::View::NARInfo;
 
+use strict;
+use warnings;
 use File::Basename;
 use Hydra::Helper::CatalystUtils;
 use MIME::Base64;
@@ -7,7 +9,6 @@ use Nix::Manifest;
 use Nix::Store;
 use Nix::Utils;
 use base qw/Catalyst::View/;
-use strict;
 
 sub process {
     my ($self, $c) = @_;
diff --git a/src/lib/Hydra/View/NixClosure.pm b/src/lib/Hydra/View/NixClosure.pm
index d906dce3..c157af6b 100644
--- a/src/lib/Hydra/View/NixClosure.pm
+++ b/src/lib/Hydra/View/NixClosure.pm
@@ -1,6 +1,7 @@
 package Hydra::View::NixClosure;
 
 use strict;
+use warnings;
 use base qw/Catalyst::View/;
 use IO::Pipe;
 
diff --git a/src/lib/Hydra/View/NixExprs.pm b/src/lib/Hydra/View/NixExprs.pm
index 194c51ec..eb68c8bc 100644
--- a/src/lib/Hydra/View/NixExprs.pm
+++ b/src/lib/Hydra/View/NixExprs.pm
@@ -1,6 +1,7 @@
 package Hydra::View::NixExprs;
 
 use strict;
+use warnings;
 use base qw/Catalyst::View/;
 use Hydra::Helper::Nix;
 use Hydra::Helper::Escape;
diff --git a/src/lib/Hydra/View/NixLog.pm b/src/lib/Hydra/View/NixLog.pm
index fb9e0e1f..c2146bd4 100644
--- a/src/lib/Hydra/View/NixLog.pm
+++ b/src/lib/Hydra/View/NixLog.pm
@@ -1,6 +1,7 @@
 package Hydra::View::NixLog;
 
 use strict;
+use warnings;
 use base qw/Catalyst::View/;
 use Hydra::Helper::CatalystUtils;
 
diff --git a/src/lib/Hydra/View/NixManifest.pm b/src/lib/Hydra/View/NixManifest.pm
index c64f8dab..5b02ac06 100644
--- a/src/lib/Hydra/View/NixManifest.pm
+++ b/src/lib/Hydra/View/NixManifest.pm
@@ -1,6 +1,7 @@
 package Hydra::View::NixManifest;
 
 use strict;
+use warnings;
 use base qw/Catalyst::View/;
 use Hydra::Helper::Nix;
 use Nix::Store;
diff --git a/src/lib/Hydra/View/NixNAR.pm b/src/lib/Hydra/View/NixNAR.pm
index e1798275..cae43275 100644
--- a/src/lib/Hydra/View/NixNAR.pm
+++ b/src/lib/Hydra/View/NixNAR.pm
@@ -1,6 +1,7 @@
 package Hydra::View::NixNAR;
 
 use strict;
+use warnings;
 use base qw/Catalyst::View/;
 use Hydra::Helper::CatalystUtils;
 
diff --git a/src/lib/Hydra/View/TT.pm b/src/lib/Hydra/View/TT.pm
index f8b3fb64..c6176231 100644
--- a/src/lib/Hydra/View/TT.pm
+++ b/src/lib/Hydra/View/TT.pm
@@ -1,6 +1,7 @@
 package Hydra::View::TT;
 
 use strict;
+use warnings;
 use base 'Catalyst::View::TT';
 use Hydra::Helper::Nix;
 use Time::Seconds;
diff --git a/src/script/hydra-backfill-ids b/src/script/hydra-backfill-ids
index d9fc362a..bb750829 100755
--- a/src/script/hydra-backfill-ids
+++ b/src/script/hydra-backfill-ids
@@ -1,6 +1,7 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use utf8;
 use Hydra::Model::DB;
 
diff --git a/src/script/hydra-create-user b/src/script/hydra-create-user
index 0ed51bd8..d0178dc1 100755
--- a/src/script/hydra-create-user
+++ b/src/script/hydra-create-user
@@ -1,6 +1,7 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use Hydra::Schema;
 use Hydra::Helper::Nix;
 use Hydra::Model::DB;
diff --git a/src/script/hydra-dev-server b/src/script/hydra-dev-server
index 4f03ee39..ea502d89 100755
--- a/src/script/hydra-dev-server
+++ b/src/script/hydra-dev-server
@@ -1,5 +1,8 @@
 #! /usr/bin/env perl
 
+use strict;
+use warnings;
+
 BEGIN {
     $ENV{CATALYST_SCRIPT_GEN} = 40;
 }
diff --git a/src/script/hydra-eval-jobset b/src/script/hydra-eval-jobset
index 77938c85..4a165d86 100755
--- a/src/script/hydra-eval-jobset
+++ b/src/script/hydra-eval-jobset
@@ -1,12 +1,13 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use utf8;
 use Config::General;
 use Data::Dump qw(dump);
 use Digest::SHA qw(sha256_hex);
 use Encode;
-use File::Slurp;
+use File::Slurper qw(read_text);
 use Hydra::Helper::AddBuilds;
 use Hydra::Helper::CatalystUtils;
 use Hydra::Helper::Email;
@@ -121,7 +122,8 @@ sub fetchInputBuild {
     my $versionRE = "(?:[A-Za-z0-9\.\-]+)";
 
     my $relName = ($prevBuild->releasename or $prevBuild->nixname);
-    my $version = $2 if $relName =~ /^($pkgNameRE)-($versionRE)$/;
+    my $version;
+    $version = $2 if $relName =~ /^($pkgNameRE)-($versionRE)$/;
 
     my $mainOutput = getMainOutput($prevBuild);
 
@@ -166,7 +168,8 @@ sub fetchInputSystemBuild {
         my $versionRE = "(?:[A-Za-z0-9\.\-]+)";
 
         my $relName = ($prevBuild->releasename or $prevBuild->nixname);
-        my $version = $2 if $relName =~ /^($pkgNameRE)-($versionRE)$/;
+        my $version;
+        $version = $2 if $relName =~ /^($pkgNameRE)-($versionRE)$/;
 
         my $input =
             { storePath => getMainOutput($prevBuild)->path
@@ -568,7 +571,7 @@ sub checkJobsetWrapped {
         die "multiple alternatives for the input containing the declarative project specification are not supported\n"
             if scalar @declInputs != 1;
         my $declFile = $declInput->{storePath} . "/" . $project->declfile;
-        my $declText = read_file($declFile)
+        my $declText = read_text($declFile)
             or die "Couldn't read declarative specification file $declFile: $!\n";
         my $declSpec;
         eval {
diff --git a/src/script/hydra-init b/src/script/hydra-init
index ac9d4afe..f0914439 100755
--- a/src/script/hydra-init
+++ b/src/script/hydra-init
@@ -1,10 +1,11 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use Hydra::Schema;
 use Hydra::Helper::Nix;
 use Hydra::Model::DB;
-use File::Slurp;
+use File::Slurper qw(read_text);
 use SQL::SplitStatement;
 use List::Util qw(max);
 
@@ -24,7 +25,7 @@ my $maxSchemaVersion = max (map { /.*\/upgrade-(\d.*)\.sql/; $1 } (glob "$home/s
 my @tables = $dbh->tables;
 if (! grep { /SchemaVersion/i } @tables) {
     print STDERR "initialising the Hydra database schema...\n";
-    my $schema = read_file(
+    my $schema = read_text(
         $dbh->{Driver}->{Name} eq 'Pg' ? "$home/sql/hydra.sql" :
         die "unsupported database type $dbh->{Driver}->{Name}\n");
     my @statements = $sql_splitter->split($schema);
@@ -57,7 +58,7 @@ QUOTE
 for (my $n = $schemaVersion; $n < $maxSchemaVersion; $n++) {
     my $m = $n + 1;
     print STDERR "upgrading Hydra schema from version $n to $m\n";
-    my $schema = read_file("$home/sql/upgrade-$m.sql");
+    my $schema = read_text("$home/sql/upgrade-$m.sql");
     my @statements = $sql_splitter->split($schema);
     eval {
         $dbh->begin_work;
diff --git a/src/script/hydra-notify b/src/script/hydra-notify
index ec95a144..c682d03d 100755
--- a/src/script/hydra-notify
+++ b/src/script/hydra-notify
@@ -1,6 +1,7 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use utf8;
 use Getopt::Long;
 use HTTP::Server::PSGI;
diff --git a/src/script/hydra-s3-backup-collect-garbage b/src/script/hydra-s3-backup-collect-garbage
index ae6423f7..23b50c2f 100755
--- a/src/script/hydra-s3-backup-collect-garbage
+++ b/src/script/hydra-s3-backup-collect-garbage
@@ -1,6 +1,7 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use File::Basename;
 use Fcntl;
 use IO::File;
@@ -25,9 +26,9 @@ my $client = Net::Amazon::S3::Client->new( s3 => Net::Amazon::S3->new( retry =>
 my $db = Hydra::Model::DB->new();
 
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-my @roots = readdir DIR;
-closedir DIR;
+opendir my $dir, $gcRootsDir or die;
+my @roots = readdir $dir;
+closedir $dir;
 
 my @actual_roots = ();
 foreach my $link (@roots) {
diff --git a/src/script/hydra-send-stats b/src/script/hydra-send-stats
index d07d9406..85807631 100755
--- a/src/script/hydra-send-stats
+++ b/src/script/hydra-send-stats
@@ -1,10 +1,11 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use utf8;
 use Hydra::Helper::Nix;
 use Net::Statsd;
-use File::Slurp;
+use File::Slurper qw(read_text);
 use JSON;
 use Getopt::Long qw(:config gnu_getopt);
 
@@ -92,7 +93,7 @@ while (1) {
         1;
     } or do { warn "$@"; };
 
-    my $meminfo = read_file("/proc/meminfo", err_mode => 'quiet') // "";
+    my $meminfo = read_text("/proc/meminfo") // "";
     $meminfo =~ m/Dirty:\s*(\d+) kB/;
     if (defined $1) {
         my $dirty = $1 / (1024.0 * 1024.0);
diff --git a/src/script/hydra-server b/src/script/hydra-server
index b8922e93..7f0deb2e 100755
--- a/src/script/hydra-server
+++ b/src/script/hydra-server
@@ -1,5 +1,8 @@
 #! /usr/bin/env perl
 
+use strict;
+use warnings;
+
 BEGIN {
     $ENV{CATALYST_SCRIPT_GEN} = 40;
 }
diff --git a/src/script/hydra-update-gc-roots b/src/script/hydra-update-gc-roots
index de544e53..b8ddf971 100755
--- a/src/script/hydra-update-gc-roots
+++ b/src/script/hydra-update-gc-roots
@@ -1,6 +1,7 @@
 #! /usr/bin/env perl
 
 use strict;
+use warnings;
 use File::Path;
 use File::stat;
 use File::Basename;
@@ -62,9 +63,9 @@ sub keepBuild {
 # Read the current GC roots.
 print STDERR "*** reading current roots...\n";
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-my @roots = readdir DIR;
-closedir DIR;
+opendir my $dir, $gcRootsDir or die;
+my @roots = readdir $dir;
+closedir $dir;
 
 
 # For scheduled builds, we register the derivation as a GC root.
diff --git a/src/sql/update-dbix.pl b/src/sql/update-dbix.pl
index 97061f21..8490ca3c 100644
--- a/src/sql/update-dbix.pl
+++ b/src/sql/update-dbix.pl
@@ -1,4 +1,6 @@
 use Cwd;
+use strict;
+use warnings;
 
 die "$0: dbi connection string required \n" if scalar @ARGV != 1;
 
diff --git a/t/Config/hydra-notify.t b/t/Config/hydra-notify.t
index 7fc8aa63..fb050324 100644
--- a/t/Config/hydra-notify.t
+++ b/t/Config/hydra-notify.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init(hydra_config => q|
diff --git a/t/Config/include.t b/t/Config/include.t
index 3e57b3d4..e161902e 100644
--- a/t/Config/include.t
+++ b/t/Config/include.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init(
diff --git a/t/Config/statsd.t b/t/Config/statsd.t
index be042127..c50e8d99 100644
--- a/t/Config/statsd.t
+++ b/t/Config/statsd.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init(hydra_config => q|
diff --git a/t/Controller/Build/evals.t b/t/Controller/Build/evals.t
index b12e00c6..6cbdeac9 100644
--- a/t/Controller/Build/evals.t
+++ b/t/Controller/Build/evals.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use Data::Dumper;
 my %ctx = test_init();
diff --git a/t/Controller/Jobset/channel.t b/t/Controller/Jobset/channel.t
index cb0a5952..322abc92 100644
--- a/t/Controller/Jobset/channel.t
+++ b/t/Controller/Jobset/channel.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 use IO::Uncompress::Bunzip2 qw(bunzip2);
 use Archive::Tar;
diff --git a/t/Controller/Jobset/evals.t b/t/Controller/Jobset/evals.t
index ba53124a..221efb65 100644
--- a/t/Controller/Jobset/evals.t
+++ b/t/Controller/Jobset/evals.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use Data::Dumper;
 my %ctx = test_init();
diff --git a/t/Controller/Jobset/http.t b/t/Controller/Jobset/http.t
index be2950f0..6b5788c5 100644
--- a/t/Controller/Jobset/http.t
+++ b/t/Controller/Jobset/http.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 use JSON qw(decode_json encode_json);
 
diff --git a/t/Controller/Jobset/type-constraints.t b/t/Controller/Jobset/type-constraints.t
index 361c7c56..88a8e2ee 100644
--- a/t/Controller/Jobset/type-constraints.t
+++ b/t/Controller/Jobset/type-constraints.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 my %ctx = test_init();
 
diff --git a/t/Controller/Root/evals.t b/t/Controller/Root/evals.t
index 895ef424..2119725b 100644
--- a/t/Controller/Root/evals.t
+++ b/t/Controller/Root/evals.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use Data::Dumper;
 my %ctx = test_init();
diff --git a/t/Controller/metrics.t b/t/Controller/metrics.t
index 8915104d..325efad9 100644
--- a/t/Controller/metrics.t
+++ b/t/Controller/metrics.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 use JSON qw(decode_json encode_json);
 
diff --git a/t/Controller/projects.t b/t/Controller/projects.t
index fb7df6ad..068f566b 100644
--- a/t/Controller/projects.t
+++ b/t/Controller/projects.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 use JSON qw(decode_json encode_json);
 
diff --git a/t/Event.t b/t/Event.t
index a15b95ea..908c2440 100644
--- a/t/Event.t
+++ b/t/Event.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Hydra::Event;
 
 use Test2::V0;
diff --git a/t/Event/BuildFinished.t b/t/Event/BuildFinished.t
index 8650f95c..298b4162 100644
--- a/t/Event/BuildFinished.t
+++ b/t/Event/BuildFinished.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/Event/BuildStarted.t b/t/Event/BuildStarted.t
index 04a7df54..08433d8d 100644
--- a/t/Event/BuildStarted.t
+++ b/t/Event/BuildStarted.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/Event/StepFinished.t b/t/Event/StepFinished.t
index a4bc3fb9..ae2d8081 100644
--- a/t/Event/StepFinished.t
+++ b/t/Event/StepFinished.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/Helper/escape.t b/t/Helper/escape.t
index 22dd4d47..424c9198 100644
--- a/t/Helper/escape.t
+++ b/t/Helper/escape.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use Data::Dumper;
 use Test2::V0;
diff --git a/t/PostgresListener.t b/t/PostgresListener.t
index ac9ec502..0249d498 100644
--- a/t/PostgresListener.t
+++ b/t/PostgresListener.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/Schema/Users.t b/t/Schema/Users.t
index fd1a66e1..b9d52419 100644
--- a/t/Schema/Users.t
+++ b/t/Schema/Users.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/api-test.t b/t/api-test.t
index ac1e4964..3fee0264 100644
--- a/t/api-test.t
+++ b/t/api-test.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use JSON;
 use File::Copy;
diff --git a/t/build-products.t b/t/build-products.t
index 6987b9df..3bc62d2e 100644
--- a/t/build-products.t
+++ b/t/build-products.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/evaluate-basic.t b/t/evaluate-basic.t
index c12709b2..f4c6fde8 100644
--- a/t/evaluate-basic.t
+++ b/t/evaluate-basic.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/evaluate-dependent-jobsets.t b/t/evaluate-dependent-jobsets.t
index c5a4085d..19c62891 100644
--- a/t/evaluate-dependent-jobsets.t
+++ b/t/evaluate-dependent-jobsets.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/input-types/bzr-checkout.t b/t/input-types/bzr-checkout.t
index ee1f90a0..297c9bd6 100644
--- a/t/input-types/bzr-checkout.t
+++ b/t/input-types/bzr-checkout.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/bzr.t b/t/input-types/bzr.t
index 0cc0a23d..36448103 100644
--- a/t/input-types/bzr.t
+++ b/t/input-types/bzr.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/darcs.t b/t/input-types/darcs.t
index aa95a8e6..7f8bd044 100644
--- a/t/input-types/darcs.t
+++ b/t/input-types/darcs.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/deepgit.t b/t/input-types/deepgit.t
index 4d418148..487d0a83 100644
--- a/t/input-types/deepgit.t
+++ b/t/input-types/deepgit.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/git-rev.t b/t/input-types/git-rev.t
index 866370d2..a1749f3b 100644
--- a/t/input-types/git-rev.t
+++ b/t/input-types/git-rev.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/git.t b/t/input-types/git.t
index 0804cc1a..ed2ab43b 100644
--- a/t/input-types/git.t
+++ b/t/input-types/git.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/hg.t b/t/input-types/hg.t
index 28552288..83d9df87 100644
--- a/t/input-types/hg.t
+++ b/t/input-types/hg.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/svn-checkout.t b/t/input-types/svn-checkout.t
index 48f07f09..af4e65ce 100644
--- a/t/input-types/svn-checkout.t
+++ b/t/input-types/svn-checkout.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/input-types/svn.t b/t/input-types/svn.t
index c2eb8cec..44f8d44e 100644
--- a/t/input-types/svn.t
+++ b/t/input-types/svn.t
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use Setup;
 use TestScmInput;
 
diff --git a/t/lib/Setup.pm b/t/lib/Setup.pm
index 800c90eb..b80eea14 100644
--- a/t/lib/Setup.pm
+++ b/t/lib/Setup.pm
@@ -1,6 +1,7 @@
 package Setup;
 
 use strict;
+use warnings;
 use Exporter;
 use Test::PostgreSQL;
 use File::Temp;
@@ -49,7 +50,7 @@ sub test_init {
     $ENV{'NIX_CONF_DIR'} = "$dir/nix/etc/nix";
     make_path($ENV{'NIX_CONF_DIR'});
     my $nixconf = "$ENV{'NIX_CONF_DIR'}/nix.conf";
-    my $nix_config = "sandbox = false\n" . $opts{'nix_config'};
+    my $nix_config = "sandbox = false\n" . ($opts{'nix_config'} || "");
     write_file($nixconf, $nix_config);
     $ENV{'HYDRA_CONFIG'} = "$dir/hydra.conf";
 
diff --git a/t/queue-runner/default-machine-file.t b/t/queue-runner/default-machine-file.t
index d57f1816..e6348226 100644
--- a/t/queue-runner/default-machine-file.t
+++ b/t/queue-runner/default-machine-file.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init(
diff --git a/t/s3-backup-test.pl b/t/s3-backup-test.pl
index 372a9697..9332ab15 100644
--- a/t/s3-backup-test.pl
+++ b/t/s3-backup-test.pl
@@ -1,4 +1,5 @@
 use strict;
+use warnings;
 use File::Basename;
 use Hydra::Model::DB;
 use Hydra::Helper::Nix;
@@ -38,12 +39,12 @@ ok(-e "/tmp/s3/hydra/$successful_hash.nar", "The nar of a build that's a root is
 ok(-e "/tmp/s3/hydra/$successful_hash.narinfo", "The narinfo of a build that's a root is not removed by gc");
 
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-while(readdir DIR) {
-    next if $_ eq "." or $_ eq "..";
-    unlink "$gcRootsDir/$_";
+opendir my $dir, $gcRootsDir or die;
+while(my $file = readdir $dir) {
+    next if $file eq "." or $file eq "..";
+    unlink "$gcRootsDir/$file";
 }
-closedir DIR;
+closedir $dir;
 system("hydra-s3-backup-collect-garbage");
 ok(not -e "/tmp/s3/hydra/$successful_hash.nar", "The nar of a build that's not a root is removed by gc");
 ok(not -e "/tmp/s3/hydra/$successful_hash.narinfo", "The narinfo of a build that's not a root is removed by gc");
diff --git a/t/scripts/hydra-create-user.t b/t/scripts/hydra-create-user.t
index 3706d911..abd0b1b8 100644
--- a/t/scripts/hydra-create-user.t
+++ b/t/scripts/hydra-create-user.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/scripts/hydra-init.t b/t/scripts/hydra-init.t
index 517a14d7..3fbcb629 100644
--- a/t/scripts/hydra-init.t
+++ b/t/scripts/hydra-init.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/scripts/hydra-send-stats.t b/t/scripts/hydra-send-stats.t
index dde88cfe..1c0e1eeb 100644
--- a/t/scripts/hydra-send-stats.t
+++ b/t/scripts/hydra-send-stats.t
@@ -1,5 +1,6 @@
 use feature 'unicode_strings';
 use strict;
+use warnings;
 use Setup;
 
 my %ctx = test_init();
diff --git a/t/setup-notifications-jobset.pl b/t/setup-notifications-jobset.pl
index 8eef78e6..70998845 100644
--- a/t/setup-notifications-jobset.pl
+++ b/t/setup-notifications-jobset.pl
@@ -1,3 +1,5 @@
+use strict;
+use warnings;
 use LWP::UserAgent;
 use JSON;