diff --git a/api/logic/CMakeLists.txt b/api/logic/CMakeLists.txt
index 17e22458..6d269714 100644
--- a/api/logic/CMakeLists.txt
+++ b/api/logic/CMakeLists.txt
@@ -246,6 +246,8 @@ set(MINECRAFT_SOURCES
     minecraft/launch/ReconstructAssets.h
     minecraft/launch/ScanModFolders.cpp
     minecraft/launch/ScanModFolders.h
+    minecraft/launch/VerifyJavaInstall.cpp
+    minecraft/launch/VerifyJavaInstall.h
 
     minecraft/legacy/LegacyModList.h
     minecraft/legacy/LegacyModList.cpp
diff --git a/api/logic/minecraft/MinecraftInstance.cpp b/api/logic/minecraft/MinecraftInstance.cpp
index fdf9bd61..ea1e47b6 100644
--- a/api/logic/minecraft/MinecraftInstance.cpp
+++ b/api/logic/minecraft/MinecraftInstance.cpp
@@ -23,6 +23,7 @@
 #include "minecraft/launch/ClaimAccount.h"
 #include "minecraft/launch/ReconstructAssets.h"
 #include "minecraft/launch/ScanModFolders.h"
+#include "minecraft/launch/VerifyJavaInstall.h"
 #include "java/launch/CheckJava.h"
 #include "java/JavaUtils.h"
 #include "meta/Index.h"
@@ -915,6 +916,11 @@ shared_qobject_ptr<LaunchTask> MinecraftInstance::createLaunchTask(AuthSessionPt
         process->appendStep(new ReconstructAssets(pptr));
     }
 
+    // verify that minimum Java requirements are met
+    {
+        process->appendStep(new VerifyJavaInstall(pptr));
+    }
+
     {
         // actually launch the game
         auto method = launchMethod();
diff --git a/api/logic/minecraft/VersionFilterData.cpp b/api/logic/minecraft/VersionFilterData.cpp
index a47fc0a0..38e7b60c 100644
--- a/api/logic/minecraft/VersionFilterData.cpp
+++ b/api/logic/minecraft/VersionFilterData.cpp
@@ -65,4 +65,7 @@ VersionFilterData::VersionFilterData()
         QSet<QString>{"net.java.jinput:jinput",     "net.java.jinput:jinput-platform",
                       "net.java.jutils:jutils",     "org.lwjgl.lwjgl:lwjgl",
                       "org.lwjgl.lwjgl:lwjgl_util", "org.lwjgl.lwjgl:lwjgl-platform"};
+
+    java8BeginsDate  = timeFromS3Time("2017-03-30T09:32:19+00:00");
+    java16BeginsDate = timeFromS3Time("2021-05-12T11:19:15+00:00");
 }
diff --git a/api/logic/minecraft/VersionFilterData.h b/api/logic/minecraft/VersionFilterData.h
index afd4502b..d100acc3 100644
--- a/api/logic/minecraft/VersionFilterData.h
+++ b/api/logic/minecraft/VersionFilterData.h
@@ -23,5 +23,9 @@ struct VersionFilterData
     QDateTime legacyCutoffDate;
     // Libraries that belong to LWJGL
     QSet<QString> lwjglWhitelist;
+    // release date of first version to require Java 8 (17w13a)
+    QDateTime java8BeginsDate;
+    // release data of first version to require Java 16 (21w19a)
+    QDateTime java16BeginsDate;
 };
 extern VersionFilterData MULTIMC_LOGIC_EXPORT g_VersionFilterData;
diff --git a/api/logic/minecraft/launch/VerifyJavaInstall.cpp b/api/logic/minecraft/launch/VerifyJavaInstall.cpp
new file mode 100644
index 00000000..657669af
--- /dev/null
+++ b/api/logic/minecraft/launch/VerifyJavaInstall.cpp
@@ -0,0 +1,34 @@
+#include "VerifyJavaInstall.h"
+
+#include <launch/LaunchTask.h>
+#include <minecraft/MinecraftInstance.h>
+#include <minecraft/PackProfile.h>
+#include <minecraft/VersionFilterData.h>
+
+void VerifyJavaInstall::executeTask() {
+    auto m_inst = std::dynamic_pointer_cast<MinecraftInstance>(m_parent->instance());
+
+    auto javaVersion = m_inst->getJavaVersion();
+    auto minecraftComponent = m_inst->getPackProfile()->getComponent("net.minecraft");
+
+    // Java 16 requirement
+    if (minecraftComponent->getReleaseDateTime() >= g_VersionFilterData.java16BeginsDate) {
+        if (javaVersion.major() < 16) {
+            emit logLine("Minecraft 21w19a and above require the use of Java 16",
+                         MessageLevel::Fatal);
+            emitFailed(tr("Minecraft 21w19a and above require the use of Java 16"));
+            return;
+        }
+    }
+    // Java 8 requirement
+    else if (minecraftComponent->getReleaseDateTime() >= g_VersionFilterData.java8BeginsDate) {
+        if (javaVersion.major() < 8) {
+            emit logLine("Minecraft 17w13a and above require the use of Java 8",
+                         MessageLevel::Fatal);
+            emitFailed(tr("Minecraft 17w13a and above require the use of Java 8"));
+            return;
+        }
+    }
+
+    emitSucceeded();
+}
diff --git a/api/logic/minecraft/launch/VerifyJavaInstall.h b/api/logic/minecraft/launch/VerifyJavaInstall.h
new file mode 100644
index 00000000..a553106d
--- /dev/null
+++ b/api/logic/minecraft/launch/VerifyJavaInstall.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include <launch/LaunchStep.h>
+
+class VerifyJavaInstall : public LaunchStep {
+    Q_OBJECT
+
+public:
+    explicit VerifyJavaInstall(LaunchTask *parent) : LaunchStep(parent) {
+    };
+    ~VerifyJavaInstall() override = default;
+
+    void executeTask() override;
+    bool canAbort() const override {
+        return false;
+    }
+};
diff --git a/api/logic/modplatform/atlauncher/ATLPackInstallTask.cpp b/api/logic/modplatform/atlauncher/ATLPackInstallTask.cpp
index 89829c05..dac80e8c 100644
--- a/api/logic/modplatform/atlauncher/ATLPackInstallTask.cpp
+++ b/api/logic/modplatform/atlauncher/ATLPackInstallTask.cpp
@@ -4,6 +4,7 @@
 #include <MMCZip.h>
 #include <minecraft/OneSixVersionFormat.h>
 #include <Version.h>
+#include <net/ChecksumValidator.h>
 #include "ATLPackInstallTask.h"
 
 #include "BuildConfig.h"
@@ -407,7 +408,12 @@ void PackInstallTask::installConfigs()
     auto entry = ENV.metacache()->resolveEntry("ATLauncherPacks", path);
     entry->setStale(true);
 
-    jobPtr->addNetAction(Net::Download::makeCached(url, entry));
+    auto dl = Net::Download::makeCached(url, entry);
+    if (!m_version.configs.sha1.isEmpty()) {
+        auto rawSha1 = QByteArray::fromHex(m_version.configs.sha1.toLatin1());
+        dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Sha1, rawSha1));
+    }
+    jobPtr->addNetAction(dl);
     archivePath = entry->getFullPath();
 
     connect(jobPtr.get(), &NetJob::succeeded, this, [&]()
@@ -508,6 +514,10 @@ void PackInstallTask::downloadMods()
             modsToExtract.insert(entry->getFullPath(), mod);
 
             auto dl = Net::Download::makeCached(url, entry);
+            if (!mod.md5.isEmpty()) {
+                auto rawMd5 = QByteArray::fromHex(mod.md5.toLatin1());
+                dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Md5, rawMd5));
+            }
             jobPtr->addNetAction(dl);
         }
         else if(mod.type == ModType::Decomp) {
@@ -516,6 +526,10 @@ void PackInstallTask::downloadMods()
             modsToDecomp.insert(entry->getFullPath(), mod);
 
             auto dl = Net::Download::makeCached(url, entry);
+            if (!mod.md5.isEmpty()) {
+                auto rawMd5 = QByteArray::fromHex(mod.md5.toLatin1());
+                dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Md5, rawMd5));
+            }
             jobPtr->addNetAction(dl);
         }
         else {
@@ -526,6 +540,10 @@ void PackInstallTask::downloadMods()
             entry->setStale(true);
 
             auto dl = Net::Download::makeCached(url, entry);
+            if (!mod.md5.isEmpty()) {
+                auto rawMd5 = QByteArray::fromHex(mod.md5.toLatin1());
+                dl->addValidator(new Net::ChecksumValidator(QCryptographicHash::Md5, rawMd5));
+            }
             jobPtr->addNetAction(dl);
 
             auto path = FS::PathCombine(m_stagingPath, "minecraft", relpath, mod.file);
diff --git a/api/logic/modplatform/atlauncher/ATLPackManifest.cpp b/api/logic/modplatform/atlauncher/ATLPackManifest.cpp
index f28fd35c..e25d8346 100644
--- a/api/logic/modplatform/atlauncher/ATLPackManifest.cpp
+++ b/api/logic/modplatform/atlauncher/ATLPackManifest.cpp
@@ -109,6 +109,11 @@ static void loadVersionLibrary(ATLauncher::VersionLibrary & p, QJsonObject & obj
     p.server = Json::ensureString(obj, "server", "");
 }
 
+static void loadVersionConfigs(ATLauncher::VersionConfigs & p, QJsonObject & obj) {
+    p.filesize = Json::requireInteger(obj, "filesize");
+    p.sha1 = Json::requireString(obj, "sha1");
+}
+
 static void loadVersionMod(ATLauncher::VersionMod & p, QJsonObject & obj) {
     p.name = Json::requireString(obj, "name");
     p.version = Json::requireString(obj, "version");
@@ -195,7 +200,6 @@ void ATLauncher::loadVersion(PackVersion & v, QJsonObject & obj)
         }
     }
 
-
     if(obj.contains("mods")) {
         auto mods = Json::requireArray(obj, "mods");
         for (const auto modRaw : mods)
@@ -206,4 +210,9 @@ void ATLauncher::loadVersion(PackVersion & v, QJsonObject & obj)
             v.mods.append(mod);
         }
     }
+
+    if(obj.contains("configs")) {
+        auto configsObj = Json::requireObject(obj, "configs");
+        loadVersionConfigs(v.configs, configsObj);
+    }
 }
diff --git a/api/logic/modplatform/atlauncher/ATLPackManifest.h b/api/logic/modplatform/atlauncher/ATLPackManifest.h
index 376587b0..17821e4c 100644
--- a/api/logic/modplatform/atlauncher/ATLPackManifest.h
+++ b/api/logic/modplatform/atlauncher/ATLPackManifest.h
@@ -101,6 +101,12 @@ struct VersionMod
     bool effectively_hidden;
 };
 
+struct VersionConfigs
+{
+    int filesize;
+    QString sha1;
+};
+
 struct PackVersion
 {
     QString version;
@@ -112,6 +118,7 @@ struct PackVersion
     VersionLoader loader;
     QVector<VersionLibrary> libraries;
     QVector<VersionMod> mods;
+    VersionConfigs configs;
 };
 
 MULTIMC_LOGIC_EXPORT void loadVersion(PackVersion & v, QJsonObject & obj);
diff --git a/application/pages/modplatform/atlauncher/AtlOptionalModDialog.cpp b/application/pages/modplatform/atlauncher/AtlOptionalModDialog.cpp
index cffe5d55..14bbd18b 100644
--- a/application/pages/modplatform/atlauncher/AtlOptionalModDialog.cpp
+++ b/application/pages/modplatform/atlauncher/AtlOptionalModDialog.cpp
@@ -200,6 +200,8 @@ AtlOptionalModDialog::AtlOptionalModDialog(QWidget *parent, QVector<ATLauncher::
             listModel, &AtlOptionalModListModel::selectRecommended);
     connect(ui->clearAllButton, &QPushButton::pressed,
             listModel, &AtlOptionalModListModel::clearAll);
+    connect(ui->installButton, &QPushButton::pressed,
+            this, &QDialog::close);
 }
 
 AtlOptionalModDialog::~AtlOptionalModDialog() {