What causes "%s class prefix only allows alphanumeric characters." in OpenAPITools/openapi-generator?

Use a purely alphanumeric prefix, e.g. -DapiModulePrefix=Acme.

OpenAPITools/openapi-generator · error · IllegalArgumentException

%s class prefix only allows alphanumeric characters.

Error message

%s class prefix only allows alphanumeric characters.

What it means

Class-prefix options (apiModulePrefix, configurationPrefix) are validated for alphanumeric-only content, because the prefix is concatenated into generated class names such as ApiModule and Configuration. Non-alphanumeric characters would produce invalid TypeScript identifiers.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptAngularClientCodegen.java:679

     */
    private void validateFileSuffixArgument(String argument, String value) {
        if (!value.matches(FILE_NAME_SUFFIX_PATTERN)) {
            throw new IllegalArgumentException(
                    String.format(Locale.ROOT, "%s file suffix only allows '.', '-' and alphanumeric characters.", argument)
            );
        }
    }

    /**
     * Validates that the given string value only contains alpha numeric characters.
     * Throws an IllegalArgumentException, if the string contains any other characters.
     *
     * @param argument The name of the argument being validated. This is only used for displaying an error message.
     * @param value    The value that is being validated.
     */
    private void validateClassPrefixArgument(String argument, String value) {
        if (!value.matches(CLASS_NAME_PREFIX_PATTERN)) {
            throw new IllegalArgumentException(
                    String.format(Locale.ROOT, "%s class prefix only allows alphanumeric characters.", argument)
            );
        }
    }

    /**
     * Validates that the given string value only contains alpha numeric characters.
     * Throws an IllegalArgumentException, if the string contains any other characters.
     *
     * @param argument The name of the argument being validated. This is only used for displaying an error message.
     * @param value    The value that is being validated.
     */
    private void validateClassSuffixArgument(String argument, String value) {
        if (!value.matches(CLASS_NAME_SUFFIX_PATTERN)) {
            throw new IllegalArgumentException(
                    String.format(Locale.ROOT, "%s class suffix only allows alphanumeric characters.", argument)
            );
        }

View on GitHub (pinned to fcec517be3)

Solutions

Use a purely alphanumeric prefix, e.g. -DapiModulePrefix=Acme.
Remove the prefix option to accept the default class names.

Example fix

# before
-DapiModulePrefix=acme-api

# after
-DapiModulePrefix=AcmeApi

Defensive patterns

Strategy: validation

Validate before calling

// node: class prefixes must be alphanumeric
const ALNUM = /^[A-Za-z0-9]+$/;
for (const [k, v] of Object.entries({ apiModulePrefix: opts.apiModulePrefix, configurationPrefix: opts.configurationPrefix }))
  if (v && !ALNUM.test(v)) throw new Error(`${k} must be alphanumeric, got: ${v}`);

Type guard

const isValidClassPrefix = (v: string): boolean => /^[A-Za-z0-9]+$/.test(v);

Try / catch

// Java
try { new DefaultGenerator().opts(input).generate(); }
catch (IllegalArgumentException e) {
    // prefix rejected: sanitize to alphanumeric (strip -._) and rerun
}

Prevention

Treat prefix options as identifier parts, not free text.
Add a config lint step for naming options before generation.
Prefer camel- or Pascal-case single-word prefixes.

When it happens

Trigger: -DapiModulePrefix=My-Api or -DconfigurationPrefix=$conf — any prefix matching outside [A-Za-z0-9]+.

Common situations: Using namespace-style prefixes with dots or dashes; pasting vendor prefixes that include symbols; monorepo naming conventions that assume hyphenated module names.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/137f272db7449db0. Report an issue: GitHub.