diff --git a/devtools/cli/src/main/java/io/quarkus/cli/ProjectExtensionsAdd.java b/devtools/cli/src/main/java/io/quarkus/cli/ProjectExtensionsAdd.java
index 3b1266ecdae524..4d3e1572d771ce 100644
--- a/devtools/cli/src/main/java/io/quarkus/cli/ProjectExtensionsAdd.java
+++ b/devtools/cli/src/main/java/io/quarkus/cli/ProjectExtensionsAdd.java
@@ -17,7 +17,7 @@ public class ProjectExtensionsAdd extends BaseBuildCommand implements Callable<I
     @CommandLine.Mixin
     RunModeOption runMode;
 
-    @CommandLine.Parameters(arity = "1", paramLabel = "EXTENSION", description = "extensions to add to this project")
+    @CommandLine.Parameters(arity = "1", paramLabel = "EXTENSION", description = "extensions to add to this project", split = ",")
     Set<String> extensions;
 
     @Override
diff --git a/devtools/cli/src/test/java/io/quarkus/cli/CliProjectExtensionsAddTest.java b/devtools/cli/src/test/java/io/quarkus/cli/CliProjectExtensionsAddTest.java
new file mode 100644
index 00000000000000..8b8769e52fc28b
--- /dev/null
+++ b/devtools/cli/src/test/java/io/quarkus/cli/CliProjectExtensionsAddTest.java
@@ -0,0 +1,111 @@
+package io.quarkus.cli;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import io.quarkus.devtools.testing.RegistryClientTestHelper;
+import picocli.CommandLine;
+
+public class CliProjectExtensionsAddTest {
+
+    static final Path testProjectRoot = Paths.get(System.getProperty("user.dir")).toAbsolutePath()
+            .resolve("target/test-project/");
+    static final Path workspaceRoot = testProjectRoot.resolve("CliProjectExtensionsAddTest");
+    Path project;
+
+    @BeforeAll
+    public static void setupTestRegistry() {
+        RegistryClientTestHelper.enableRegistryClientTestConfig();
+    }
+
+    @AfterAll
+    public static void cleanupTestRegistry() {
+        RegistryClientTestHelper.disableRegistryClientTestConfig();
+    }
+
+    @BeforeEach
+    public void setupTestDirectories() throws Exception {
+        CliDriver.deleteDir(workspaceRoot);
+    }
+
+    @Test
+    public void testAddExtensionsCommas() throws Exception {
+        CliDriver.Result result = CliDriver.execute(workspaceRoot, "create", "app", "-e", "-B", "--verbose",
+                "org.acme:quarkus-add-extensions-commas");
+        Assertions.assertEquals(CommandLine.ExitCode.OK, result.exitCode, "Expected OK return code." + result);
+        Assertions.assertTrue(result.stdout.contains("SUCCESS"),
+                "Expected confirmation that the project has been created." + result);
+
+        Path project = workspaceRoot.resolve("quarkus-add-extensions-commas");
+        Path projectPom = project.resolve("pom.xml");
+        Assertions.assertTrue(Files.exists(projectPom), "pom.xml should exist");
+
+        String pomContent = Files.readString(projectPom);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive:\n" + pomContent);
+
+        // Check the extensions are not there yet
+        Assertions.assertFalse(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jackson</artifactId>"),
+                "pom.xml should not contain quarkus-resteasy-reactive-jackson:\n" + pomContent);
+        Assertions.assertFalse(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jsonb</artifactId>"),
+                "pom.xml should not contain quarkus-resteasy-reactive-jsonb:\n" + pomContent);
+
+        // Add the extensions
+        result = CliDriver.execute(project, "extension", "add",
+                "quarkus-resteasy-reactive-jackson,quarkus-resteasy-reactive-jsonb");
+        Assertions.assertEquals(CommandLine.ExitCode.OK, result.exitCode, "Expected OK return code." + result);
+        Assertions.assertTrue(result.stdout.contains("SUCCESS"),
+                "Expected confirmation that the project has been created." + result);
+
+        // Check that they have been added
+        pomContent = Files.readString(projectPom);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jackson</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive-jackson:\n" + pomContent);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jsonb</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive-jsonb:\n" + pomContent);
+    }
+
+    @Test
+    public void testAddExtensionsSpaces() throws Exception {
+        CliDriver.Result result = CliDriver.execute(workspaceRoot, "create", "app", "-e", "-B", "--verbose",
+                "org.acme:quarkus-add-extensions-spaces");
+        Assertions.assertEquals(CommandLine.ExitCode.OK, result.exitCode, "Expected OK return code." + result);
+        Assertions.assertTrue(result.stdout.contains("SUCCESS"),
+                "Expected confirmation that the project has been created." + result);
+
+        Path project = workspaceRoot.resolve("quarkus-add-extensions-spaces");
+        Path projectPom = project.resolve("pom.xml");
+        Assertions.assertTrue(Files.exists(projectPom), "pom.xml should exist");
+
+        String pomContent = Files.readString(projectPom);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive:\n" + pomContent);
+
+        // Check the extensions are not there yet
+        Assertions.assertFalse(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jackson</artifactId>"),
+                "pom.xml should not contain quarkus-resteasy-reactive-jackson:\n" + pomContent);
+        Assertions.assertFalse(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jsonb</artifactId>"),
+                "pom.xml should not contain quarkus-resteasy-reactive-jsonb:\n" + pomContent);
+
+        // Add the extensions
+        result = CliDriver.execute(project, "extension", "add", "quarkus-resteasy-reactive-jackson",
+                "quarkus-resteasy-reactive-jsonb");
+        Assertions.assertEquals(CommandLine.ExitCode.OK, result.exitCode, "Expected OK return code." + result);
+        Assertions.assertTrue(result.stdout.contains("SUCCESS"),
+                "Expected confirmation that the project has been created." + result);
+
+        // Check that they have been added
+        pomContent = Files.readString(projectPom);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jackson</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive-jackson:\n" + pomContent);
+        Assertions.assertTrue(pomContent.contains("<artifactId>quarkus-resteasy-reactive-jsonb</artifactId>"),
+                "pom.xml should contain quarkus-resteasy-reactive-jsonb:\n" + pomContent);
+    }
+}
diff --git a/independent-projects/tools/devtools-testing/src/main/resources/fake-catalog.json b/independent-projects/tools/devtools-testing/src/main/resources/fake-catalog.json
index b6e8a6310329c6..5c65f2a6f30478 100644
--- a/independent-projects/tools/devtools-testing/src/main/resources/fake-catalog.json
+++ b/independent-projects/tools/devtools-testing/src/main/resources/fake-catalog.json
@@ -75,6 +75,62 @@
         "io.quarkus:quarkus-fake-bom:999-FAKE:json:999-FAKE"
       ]
     },
+    {
+      "name" : "RESTEasy Reactive Jackson",
+      "description" : "Jackson serialization support for RESTEasy Reactive. This extension is not compatible with the quarkus-resteasy extension, or any of the extensions that depend on it",
+      "metadata" : {
+        "codestart" : {
+          "name" : "resteasy-reactive",
+          "kind" : "core",
+          "languages" : [ "java", "kotlin", "scala" ],
+          "artifact" : "io.quarkus:quarkus-project-core-extension-codestarts::jar:3.6.1"
+        },
+        "minimum-java-version" : "11",
+        "status" : "stable",
+        "config" : [ "quarkus.resteasy-reactive.", "quarkus.jackson." ],
+        "built-with-quarkus-core" : "3.6.1",
+        "scm-url" : "https://github.com/quarkus-release/release",
+        "short-name" : "resteasy-reactive-jackson",
+        "capabilities" : {
+          "provides" : [ "io.quarkus.rest.jackson", "io.quarkus.resteasy.reactive.json.jackson" ]
+        },
+        "categories" : [ "web", "reactive" ],
+        "extension-dependencies" : [ "io.quarkus:quarkus-resteasy-reactive", "io.quarkus:quarkus-resteasy-reactive-common", "io.quarkus:quarkus-mutiny", "io.quarkus:quarkus-smallrye-context-propagation", "io.quarkus:quarkus-vertx", "io.quarkus:quarkus-netty", "io.quarkus:quarkus-vertx-http", "io.quarkus:quarkus-core", "io.quarkus:quarkus-jsonp", "io.quarkus:quarkus-virtual-threads", "io.quarkus:quarkus-arc", "io.quarkus:quarkus-resteasy-reactive-jackson-common", "io.quarkus:quarkus-jackson" ],
+        "keywords" : [ "rest-jackson", "quarkus-resteasy-reactive-json", "jaxrs-json", "rest", "jaxrs", "json", "jackson", "jakarta-rest" ]
+      },
+      "artifact" : "io.quarkus:quarkus-resteasy-reactive-jackson::jar:999-FAKE",
+      "origins": [
+        "io.quarkus:quarkus-fake-bom:999-FAKE:json:999-FAKE"
+      ]
+    },
+    {
+      "name" : "RESTEasy Reactive JSON-B",
+      "description" : "JSON-B serialization support for RESTEasy Reactive. This extension is not compatible with the quarkus-resteasy extension, or any of the extensions that depend on it.",
+      "metadata" : {
+        "codestart" : {
+          "name" : "resteasy-reactive",
+          "kind" : "core",
+          "languages" : [ "java", "kotlin", "scala" ],
+          "artifact" : "io.quarkus:quarkus-project-core-extension-codestarts::jar:3.6.1"
+        },
+        "minimum-java-version" : "11",
+        "status" : "stable",
+        "config" : [ "quarkus.resteasy-reactive." ],
+        "built-with-quarkus-core" : "3.6.1",
+        "scm-url" : "https://github.com/quarkus-release/release",
+        "short-name" : "resteasy-reactive-jsonb",
+        "capabilities" : {
+          "provides" : [ "io.quarkus.rest.jsonb", "io.quarkus.resteasy.reactive.json.jsonb" ]
+        },
+        "categories" : [ "web", "reactive" ],
+        "extension-dependencies" : [ "io.quarkus:quarkus-resteasy-reactive", "io.quarkus:quarkus-resteasy-reactive-common", "io.quarkus:quarkus-mutiny", "io.quarkus:quarkus-smallrye-context-propagation", "io.quarkus:quarkus-vertx", "io.quarkus:quarkus-netty", "io.quarkus:quarkus-vertx-http", "io.quarkus:quarkus-core", "io.quarkus:quarkus-jsonp", "io.quarkus:quarkus-virtual-threads", "io.quarkus:quarkus-arc", "io.quarkus:quarkus-resteasy-reactive-jsonb-common", "io.quarkus:quarkus-jsonb" ],
+        "keywords" : [ "rest-jsonb", "resteasy-reactive-json", "jaxrs-json", "rest", "jaxrs", "json", "jsonb", "jakarta-rest" ]
+      },
+      "artifact" : "io.quarkus:quarkus-resteasy-reactive-jsonb::jar:999-FAKE",
+      "origins": [
+        "io.quarkus:quarkus-fake-bom:999-FAKE:json:999-FAKE"
+      ]
+    },
     {
       "name": "YAML Configuration",
       "description": "Use YAML to configure your Quarkus application",