stanfordnlp/CoreNLP · error · IllegalArgumentException

-labels is required

Error message

-labels is required

What it means

The label map is central to the tool, so main validates that -labels <file> was provided and throws IllegalArgumentException("-labels is required") otherwise. Without a labels file there is no text->label mapping to apply to the trees.

Solutions

1. Add -labels <file> pointing to a TSV mapping of text to label
2. Verify the flag spelling is -labels (plural)
3. Ensure the labels file path itself is correct so a subsequent read doesn't fail

Example fix

// before
// java ParseAndSetLabels -parser m.gz -sentences s.txt -output o.txt
// after
// java ParseAndSetLabels -parser m.gz -sentences s.txt -output o.txt -labels labels.txt

java.util.List<String> a = java.util.Arrays.asList(args);
if (!a.contains("-labels")) throw new IllegalArgumentException("-labels is required");
else if (!new java.io.File(a.get(a.indexOf("-labels") + 1)).exists()) throw new IllegalArgumentException("labels file missing");

try {
  ParseAndSetLabels.main(args);
} catch (IllegalArgumentException e) {
  if ("-labels is required".equals(e.getMessage())) System.err.println("Add -labels <file> to the command line");
  throw e;
}

When it happens

Trigger: Running ParseAndSetLabels.main without the -labels flag (or with a misspelled variant that never set labelsFile).

Common situations: Forgotten flag in scheduled jobs; labels file argument dropped during script refactoring; typo such as -label instead of -labels that hits the unknown-argument branch instead.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Error: No dest file provided in properties or via command…
• Error: No training file provided in properties or via…
• Error: No training file provided in properties or via…
• Error: -train option must have treebankPath as first…
• Must specify input with -input

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/5cc93b26ef9cf5d2. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/parser/tools/ParseAndSetLabels.java:249

      } else if (args[argIndex].equalsIgnoreCase("-nouseLabelKeys")) {
        useLabelKeys = false;
        argIndex += 1;
      } else {
        throw new IllegalArgumentException("Unknown argument " + args[argIndex]);
      }
    }

    if (outputFile == null) {
      throw new IllegalArgumentException("-output is required");
    }
    if (sentencesFile == null && !useLabelKeys) {
      throw new IllegalArgumentException("-sentences or -useLabelKeys is required");
    }
    if (sentencesFile != null && useLabelKeys) {
      throw new IllegalArgumentException("Use only one of -sentences or -useLabelKeys");
    }
    if (labelsFile == null) {
      throw new IllegalArgumentException("-labels is required");
    }

    ParserGrammar parser = loadParser(parserFile, taggerFile);

    TreeBinarizer binarizer = null;
    if (binarize) {
      binarizer = TreeBinarizer.simpleTreeBinarizer(parser.getTLPParams().headFinder(), parser.treebankLanguagePack());
    }

    Map<String, String> labelMap = readLabelMap(labelsFile, separator, remapLabels);

    List<String> sentences;
    if (sentencesFile != null) {
      sentences = readSentences(sentencesFile);
    } else {
      sentences = new ArrayList<String>(labelMap.keySet());
    }

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