languagetool-org/languagetool · error · IllegalArgumentException

You cannot list unknown words when tagging only

Error message

You cannot list unknown words when tagging only

What it means

parseOptions() enforces flag exclusivity: `-u/--list-unknown` cannot be combined with `-t/--taggeronly`. When --taggeronly is parsed and list-unknown was already set (options.isListUnknown()), it throws IllegalArgumentException. Tag-only mode just tags text and does not run the spell checker that produces unknown-word lists, so the combination is rejected.

Source

Thrown at languagetool-commandline/src/main/java/org/languagetool/commandline/CommandLineParser.java:66

      } else if (args[i].equals("-v") || args[i].equals("--verbose")) {
        options.setVerbose(true);
      } else if (args[i].equals("--line-by-line")) {
        options.setLineByLine(true);
      } else if (args[i].equals("--enable-temp-off")) {
        options.setEnableTempOff(true);
      } else if (args[i].equals("--clean-overlapping")) {
        options.setCleanOverlapping(true);
      } else if (args[i].equals("--level")) {
        String level = args[++i];
        try {
          options.setLevel(JLanguageTool.Level.valueOf(level));
        } catch (IllegalArgumentException e) {
          throw new IllegalArgumentException("Unknown level '" + level + "' - currently, only 'PICKY' is supported");
        }
      } else if (args[i].equals("-t") || args[i].equals("--taggeronly")) {
        options.setTaggerOnly(true);
        if (options.isListUnknown()) {
          throw new IllegalArgumentException("You cannot list unknown words when tagging only");
        }
        if (options.isApplySuggestions()) {
          throw new IllegalArgumentException("You cannot apply suggestions when tagging only");
        }
      } else if (args[i].equals("-r") || args[i].equals("--recursive")) {
        options.setRecursive(true);
      } else if (args[i].equals("-b2") || args[i].equals("--bitext")) {
        options.setBitext(true);
      } else if (args[i].equals("-eo") || args[i].equals("--enabledonly")) {
        if (options.getDisabledRules().size() > 0) {
          throw new IllegalArgumentException("You cannot specify both disabled rules and enabledonly");
        }
        options.setUseEnabledOnly();
      } else if (args[i].equals("-d") || args[i].equals("--disable")) {
        if (options.isUseEnabledOnly()) {
          throw new IllegalArgumentException("You cannot specify both disabled rules and enabledonly");
        }
        checkArguments("-d/--disable", i, args);

View on GitHub (pinned to 2e990059ce)

Solutions

  1. Remove -u/--list-unknown if you want tagger-only mode.
  2. Remove -t/--taggeronly if you want the unknown-words list.
  3. Run two separate invocations if you need both behaviors.

Example fix

// before
languagetool -t -u -l en file.txt
// after
languagetool -t -l en file.txt
Defensive patterns

Strategy: validation

Validate before calling

boolean hasTaggerOnly = Arrays.asList(args).contains("-t") || Arrays.asList(args).contains("--taggeronly");
boolean hasListUnknown = Arrays.asList(args).contains("-u") || Arrays.asList(args).contains("--list-unknown");
if (hasTaggerOnly && hasListUnknown) throw new IllegalArgumentException("-t and -u are mutually exclusive");

Try / catch

try {
  new CommandLineParser().parseOptions(args);
} catch (IllegalArgumentException e) {
  if (e.getMessage().contains("list unknown words when tagging only")) {
    System.err.println("Remove either -t/--taggeronly or -u/--list-unknown.");
  }
}

Prevention

When it happens

Trigger: `languagetool -t -u file.txt` (or the long forms --taggeronly --list-unknown) with -u appearing before -t on the command line.

Common situations: Script merging two previous invocations' flags; users assuming the flags are independent; documentation examples concatenated.

Understand the failure class

Background: "mutually exclusive" flag errors: what "can't supply both nx and xx", "--raw is not compatible with -i" and "cannot be used with" mean, and how to fix them — this error's family across 29 libraries.

Related errors

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/4c9fa202eaad17fd. Report an issue: GitHub.