languagetool-org/languagetool · critical · RuntimeException

Could not activate rules

Error message

Could not activate rules

What it means

The JLanguageTool constructor loads and activates the language's builtin rules (pattern rules, false friends, optional language-model rules). Any Exception during that setup is rethrown as this RuntimeException, so an instance could not be fully initialized with its rules.

Source

Thrown at languagetool-core/src/main/java/org/languagetool/JLanguageTool.java:364

    this.userConfig = Objects.requireNonNullElseGet(userConfig, UserConfig::new);
    this.globalConfig = globalConfig;
    this.cleanOverlappingMatches = true;
    ResourceBundle messages = ResourceBundleTools.getMessageBundle(language);
    if (customRules != null) {
      builtinRules = new ArrayList<>(customRules);
    } else {
      builtinRules = getAllBuiltinRules(language, messages, userConfig, globalConfig);
      try {
        activateDefaultPatternRules();
        if (!language.hasNGramFalseFriendRule(motherTongue)) {
          // use the old false friends, which always match, not depending on context
          activateDefaultFalseFriendRules();
        }
        if (!withLanguageModel) {
          updateOptionalLanguageModelRules(null); // start out with rules without language model
        }
      } catch (Exception e) {
        throw new RuntimeException("Could not activate rules", e);
      }
    }
    this.cache = cache;
    descProvider = new ShortDescriptionProvider();
    this.inputLogging = inputLogging;
  }

  /**
   * Create a JLanguageTool and setup the built-in rules for the
   * given language and false friend rules for the text language / mother tongue pair.
   *
   * @param language     the language of the text to be checked
   * @param motherTongue the user's mother tongue, used for false friend rules, or <code>null</code>.
   *                     The mother tongue may also be used as a source language for checking bilingual texts.
   * @param cache        a cache to speed up checking if the same sentences get checked more than once,
   *                     e.g. when LT is running as a server and texts are re-checked due to changes
   * @since 4.2
   */

View on GitHub (pinned to 2e990059ce)

Solutions

1. Inspect the 'Caused by' chain — it names the rule/resource that failed to load.
2. Verify all LanguageTool jars are the same version (no mixed core/language-module versions).
3. Re-download/rebuild the distribution to restore corrupted rule XML resources.
4. If a custom Language/Rules implementation is involved, test getRelevantRules() in isolation.

Example fix

// before
JLanguageTool lt = new JLanguageTool(new MyCustomLanguage());
// after (verify builtin rules load cleanly first)
JLanguageTool lt = new JLanguageTool(Languages.getLanguageForShortCode("en-US"));

try {
  Language lang = Languages.getLanguageForShortCode(code);
  // smoke-test instance creation at startup, not on first request
  try (JLanguageTool lt = new JLanguageTool(lang)) { }
} catch (RuntimeException e) {
  throw new IllegalStateException("LanguageTool init failed: " + e.getCause(), e);
}

try {
  lt = new JLanguageTool(language);
} catch (RuntimeException e) {
  logger.error("Rule activation failed", e.getCause());
  throw e; // instance is unusable; fail fast
}

When it happens

Trigger: Constructing new JLanguageTool(lang) (or with config/cache variants) when rule loading fails: broken XML grammar rules for the language, missing resource files, activateDefaultFalseFriendRules or updateOptionalLanguageModelRules throwing.

Common situations: Corrupted or partial languagetool-core resource deployment; a language module whose rule XML fails to parse; classpath issues after an upgrade leaving mixed jar versions; custom language implementations with faulty getRelevantRules.

Related errors

• Could not load language model capable rules.
• Could not create LanguageTool instance for language <languag
• Could not get rules of language <language>
• Could not check text in file <file>
• No rules are active. Please make sure your rule ids (<option

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/76e9a099affd9667. Report an issue: GitHub.