languagetool-org/languagetool · error · PathNotFoundException

Rule '<ruleId>' not found for language <lang> (LanguageTool

Error message

Rule '<ruleId>' not found for language <lang> (LanguageTool version/date: <VERSION>/<BUILD_DATE>, total rules of language: <rules.size>)

What it means

After building the rule set for the requested language, handleRuleExamplesRequest filters rules by id and, if none match, throws a PathNotFoundException naming the rule, the language, the LanguageTool version/build date, and the total rule count. This means the requested rule id simply does not exist for that language.

Source

Thrown at languagetool-server/src/main/java/org/languagetool/server/ApiV2.java:285

      throw new BadRequestException("'lang' parameter missing");
    }
    if (params.get("ruleId") == null) {
      throw new BadRequestException("'ruleId' parameter missing");
    }
    Language lang = Languages.getLanguageForShortCode(params.get("lang"));
    JLanguageTool lt = new JLanguageTool(lang);
    if (textChecker.config.languageModelDir != null) {
      lt.activateLanguageModelRules(textChecker.config.languageModelDir);
    }
    List<Rule> rules = lt.getAllRules();
    List<Rule> foundRules = new ArrayList<>();
    for (Rule rule : rules) {
      if (rule.getId().equals(params.get("ruleId"))) {
        foundRules.add(rule);
      }
    }
    if (foundRules.isEmpty()) {
      throw new PathNotFoundException("Rule '" + params.get("ruleId") + "' not found for language " + lang +
              " (LanguageTool version/date: " + JLanguageTool.VERSION + "/" + JLanguageTool.BUILD_DATE + ", total rules of language: " + rules.size() + ")");
    }
    StringWriter sw = new StringWriter();
    try (JsonGenerator g = factory.createGenerator(sw)) {
      g.writeStartObject();
      g.writeArrayFieldStart("results");
      g.writeStartObject();
      g.writeStringField("warning", "*** This is not a public API - it may change anytime ***");
      g.writeEndObject();
      for (Rule foundRule : foundRules) {
        for (CorrectExample example : foundRule.getCorrectExamples()) {
          g.writeStartObject();
          g.writeStringField("status", "correct");
          g.writeStringField("sentence", example.getExample());
          g.writeEndObject();
        }
        for (IncorrectExample example : foundRule.getIncorrectExamples()) {
          g.writeStartObject();

View on GitHub (pinned to 2e990059ce)

Solutions

1. Verify the rule id exists for the given language via GET /v2/rules?lang=<lang> before requesting examples.
2. Fix typos in the ruleId — ids are case-sensitive.
3. If the rule is language-specific, request it with the correct 'lang' short code.
4. If the rule disappeared after a LanguageTool upgrade, consult the version/date in the message and update your integration to the new rule id.

Example fix

// before
GET /v2/ruleExamples?lang=de-DE&ruleId=EN_A_VS_AN
// after
GET /v2/ruleExamples?lang=en-US&ruleId=EN_A_VS_AN

const rules = await fetch(`${base}/v2/rules?lang=${lang}`).then(r => r.json());
if (!rules.rules.some(r => r.id === ruleId)) throw new Error(`Rule ${ruleId} does not exist for ${lang}`);

// HTTP 404 with body: { error: { message: "Rule 'X' not found for language Y ..." } }
try {
  const res = await fetch(examplesUrl);
  if (res.status === 404) {
    const body = await res.json();
    console.warn('Rule not found:', body.error?.message);
  } else {
    return res.json();
  }
} catch (e) { /* network error handling */ }

When it happens

Trigger: GET /v2/ruleExamples?lang=de-DE&ruleId=EN_A_POSSESSIVE_ITS (an English-only rule asked for German); typo in the rule id; rule removed or renamed in a newer LanguageTool version.

Common situations: Hard-coded rule ids copied from another language; rules that only exist when specific grammar rules or ngram/language models are activated; clients not re-checking rule availability after a server upgrade.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Missing 'text' or 'data' parameter
• Use parameter 'dicts', not 'dict' in GET /words API method.
• 'lang' parameter missing
• 'ruleId' parameter missing
• Expected Basic Authentication

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/e5aa19a6cf6d2fd0. Report an issue: GitHub.