quarkusio/quarkus · error · IllegalArgumentException

Choose a valid build tool. Accepted values are: ${validBuild

Error message

Choose a valid build tool. Accepted values are: ${validBuildTools}

What it means

The `create` mojo accepts a `-DbuildTool` parameter which must be one of the known BuildTool values (maven, gradle, gradle-kotlin-dsl). BuildTool.findTool() returns null for anything else, and the mojo throws an IllegalArgumentException listing the accepted values. This validates the build tool selection before scaffolding starts.

Source

Thrown at devtools/maven/src/main/java/io/quarkus/maven/CreateProjectMojo.java:263

        final MojoMessageWriter log = new MojoMessageWriter(getLog());
        ExtensionCatalogResolver catalogResolver = getExtensionCatalogResolver(mvn, log);
        ExtensionCatalog catalog = resolveExtensionsCatalog(this, bomGroupId, bomArtifactId, bomVersion, stream,
                catalogResolver, mvn, log);

        File projectRoot = outputDirectory;
        File pom = project != null ? project.getFile() : null;
        Model parentPomModel = null;

        boolean containsAtLeastOneGradleFile = false;
        for (String gradleFile : Arrays.asList("build.gradle", "settings.gradle", "build.gradle.kts", "settings.gradle.kts")) {
            containsAtLeastOneGradleFile |= new File(projectRoot, gradleFile).isFile();
        }

        BuildTool buildToolEnum = BuildTool.findTool(buildTool);
        if (buildToolEnum == null) {
            String validBuildTools = String.join(",",
                    Arrays.asList(BuildTool.values()).stream().map(BuildTool::toString).collect(Collectors.toList()));
            throw new IllegalArgumentException("Choose a valid build tool. Accepted values are: " + validBuildTools);
        }
        if (BuildTool.MAVEN.equals(buildToolEnum)) {
            if (pom != null && pom.isFile()) {
                try {
                    parentPomModel = MojoUtils.readPom(pom);
                    if (!"pom".equals(parentPomModel.getPackaging())) {
                        throw new MojoExecutionException(
                                "The parent project must have a packaging type of POM. Current packaging: "
                                        + parentPomModel.getPackaging());
                    }
                } catch (IOException e) {
                    throw new MojoExecutionException("Could not access parent pom.", e);
                }
            } else if (containsAtLeastOneGradleFile) {
                throw new MojoExecutionException(
                        "You are trying to create a Maven project in a directory that contains only Gradle build files.");
            }
        } else if (BuildTool.GRADLE.equals(buildToolEnum) || BuildTool.GRADLE_KOTLIN_DSL.equals(buildToolEnum)) {

View on GitHub (pinned to e1c734241f)

Solutions

1. Use one of the listed accepted values, e.g. `-DbuildTool=maven`, `-DbuildTool=gradle`, or `-DbuildTool=gradle-kotlin-dsl`
2. Check spelling and case of the buildTool value
3. Omit `-DbuildTool` entirely to accept the default (maven)
4. If scripted, print/echo the variable being passed to confirm it is not empty

Example fix

// before
mvn io.quarkus:quarkus-maven-plugin:create -DbuildTool=Gradle
// after
mvn io.quarkus:quarkus-maven-plugin:create -DbuildTool=gradle

Set<String> valid = Set.of("maven", "gradle", "gradle-kotlin-dsl");
if (!valid.contains(buildTool)) throw new IllegalArgumentException("buildTool must be one of " + valid);

try {
    runCreateGoal(buildTool);
} catch (IllegalArgumentException e) {
    if (e.getMessage().startsWith("Choose a valid build tool")) {
        System.err.println(e.getMessage()); // lists accepted values
    }
}

When it happens

Trigger: Invoking `mvn quarkus:create -DbuildTool=<invalid>` or choosing an unsupported tool via the Quarkus CLI/code.quarkus.io flow that passes an unrecognized buildTool string.

Common situations: Typos like `-DbuildTool=mavin` or `-DbuildTool=Gradle` (case-sensitive lookup), older tooling passing tool names that were renamed, or scripting that interpolates an empty buildTool value.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Extra steps left over
• Unknown start character for json value: %s
• name cannot be null
• Either location or predicate must be set
• At least one package name must be specified

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/9e4b202aa90ef248. Report an issue: GitHub.