diff --git a/buildSrc/src/main/kotlin/pklFatJar.gradle.kts b/buildSrc/src/main/kotlin/pklFatJar.gradle.kts
index 0e519681..57fe1147 100644
--- a/buildSrc/src/main/kotlin/pklFatJar.gradle.kts
+++ b/buildSrc/src/main/kotlin/pklFatJar.gradle.kts
@@ -42,20 +42,20 @@ val relocations =
     "org.organicdesign.fp." to "org.pkl.thirdparty.paguro.",
     "org.snakeyaml.engine." to "org.pkl.thirdparty.snakeyaml.engine.",
     "org.msgpack." to "org.pkl.thirdparty.msgpack.",
-    "org.w3c.dom." to "org.pkl.thirdparty.w3c.dom",
+    "org.w3c.dom." to "org.pkl.thirdparty.w3c.dom.",
     "com.oracle.svm.core." to "org.pkl.thirdparty.svm.",
 
     // pkl-cli dependencies
     "org.jline." to "org.pkl.thirdparty.jline.",
     "com.github.ajalt.clikt." to "org.pkl.thirdparty.clikt.",
-    "com.github.ajalt.colormath" to "org.pkl.thirdparty.colormath.",
-    "com.github.ajalt.mordant" to "org.pkl.thirdparty.mordant",
-    "com.sun.jna" to "org.pkl.thirdparty.jna",
+    "com.github.ajalt.colormath." to "org.pkl.thirdparty.colormath.",
+    "com.github.ajalt.mordant." to "org.pkl.thirdparty.mordant.",
+    "com.sun.jna." to "org.pkl.thirdparty.jna.",
     "kotlin." to "org.pkl.thirdparty.kotlin.",
     "kotlinx." to "org.pkl.thirdparty.kotlinx.",
     "org.intellij." to "org.pkl.thirdparty.intellij.",
-    "org.fusesource.jansi." to "org.pkl.thirdparty.jansi",
-    "org.fusesource.hawtjni." to "org.pkl.thirdparty.hawtjni",
+    "org.fusesource.jansi." to "org.pkl.thirdparty.jansi.",
+    "org.fusesource.hawtjni." to "org.pkl.thirdparty.hawtjni.",
 
     // pkl-doc dependencies
     "org.commonmark." to "org.pkl.thirdparty.commonmark.",
@@ -71,6 +71,19 @@ val relocations =
     "com.squareup.kotlinpoet." to "org.pkl.thirdparty.kotlinpoet.",
   )
 
+for ((key, value) in relocations) {
+  if (!key.endsWith(".")) {
+    throw GradleException(
+      "Invalid relocation `\"$key\" to \"$value\"`: `$key` should end with a dot"
+    )
+  }
+  if (!value.endsWith(".")) {
+    throw GradleException(
+      "Invalid relocation `\"$key\" to \"$value\"`: `$value` should end with a dot"
+    )
+  }
+}
+
 val nonRelocations = listOf("com/oracle/truffle/", "org/graalvm/")
 
 tasks.shadowJar {
diff --git a/pkl-tools/pkl-tools.gradle.kts b/pkl-tools/pkl-tools.gradle.kts
index d5445405..7b433f94 100644
--- a/pkl-tools/pkl-tools.gradle.kts
+++ b/pkl-tools/pkl-tools.gradle.kts
@@ -15,6 +15,8 @@
  */
 import java.nio.charset.StandardCharsets
 import java.util.*
+import kotlin.io.path.createDirectories
+import kotlin.io.path.writeText
 
 plugins {
   pklAllProjects
@@ -65,6 +67,63 @@ val javadocJar by
 
 tasks.shadowJar { archiveBaseName.set("pkl-tools-all") }
 
+private fun Exec.configureTestStartFatJar(launcher: Provider<JavaLauncher>) {
+  dependsOn(tasks.shadowJar)
+  group = "verification"
+
+  // placeholder output to satisfy up-to-date check
+  val outputFile = layout.buildDirectory.file("testStartFatJar/${name}.txt")
+  outputs.file(outputFile)
+
+  inputs.files(tasks.shadowJar)
+  executable = launcher.get().executablePath.asFile.absolutePath
+
+  argumentProviders.add(
+    CommandLineArgumentProvider {
+      buildList {
+        add("-cp")
+        add(tasks.shadowJar.get().outputs.files.singleFile.absolutePath)
+        add("org.pkl.cli.Main")
+        add("eval")
+        add("-x")
+        add("1 + 1")
+        add("pkl:base")
+      }
+    }
+  )
+
+  doLast {
+    outputFile.get().asFile.toPath().let { file ->
+      file.parent.createDirectories()
+      file.writeText("OK")
+    }
+  }
+}
+
+val testStartFatJar by
+  tasks.registering(Exec::class) { configureTestStartFatJar(buildInfo.javaTestLauncher) }
+
+tasks.validateFatJar { dependsOn(testStartFatJar) }
+
+for (jdkTarget in buildInfo.jdkTestRange) {
+  if (buildInfo.jdkToolchainVersion == jdkTarget) {
+    tasks.register("testStartFatJarJdk${jdkTarget.asInt()}") {
+      group = "verification"
+      description = "alias for testStartFatJar"
+      dependsOn(testStartFatJar)
+    }
+  } else {
+    val task =
+      tasks.register("testStartFatJarJdk${jdkTarget.asInt()}", Exec::class) {
+        val launcher = project.javaToolchains.launcherFor { languageVersion = jdkTarget }
+        configureTestStartFatJar(launcher)
+      }
+    if (buildInfo.multiJdkTesting) {
+      tasks.validateFatJar { dependsOn(task) }
+    }
+  }
+}
+
 publishing {
   publications {
     named<MavenPublication>("fatJar") {