stanfordnlp/CoreNLP · error · RuntimeException

Expected nPrune, found:

Error message

Expected nPrune, found: 

What it means

Options.readData reads a serialized (text-format) parser Options block line by line and expects a fixed schema. Each section must start with an expected prefix; when the line does not match '^nPrune.*' it throws RuntimeException('Expected nPrune, found: ...'), meaning the file's option section is out of order or written by an incompatible format version.

Solutions

1. Use a parser model file that matches your library version (re-download the official model jar for your release).
2. Retrain/regenerate the grammar file with the current parser version.
3. Check that the file was not truncated or edited; restore from a clean copy.
4. Pin the library version to the one the model was built with (check the Options serialVersionUID / release notes).

Example fix

// before
LexicalizedParser.loadModel("old-v1-englishPCFG.ser.gz"); // with parser 3.9.x
// after
LexicalizedParser.loadModel("edu/stanford/nlp/models/lexparser/englishPCFG.ser.gz"); // matching version

try (BufferedReader in = Files.newBufferedReader(modelPath)) {
  String line;
  boolean ok = false;
  while ((line = in.readLine()) != null) if (line.startsWith("nPrune")) { ok = true; break; }
  if (!ok) throw new IllegalStateException("Model file options section missing nPrune line: " + modelPath);
}

try {
  parser = LexicalizedParser.loadModel(path);
} catch (RuntimeException e) {
  if (e.getMessage().startsWith("Expected nPrune")) {
    throw new IOException("Incompatible/corrupt model file: " + path, e);
  }
  throw e;
}

When it happens

Trigger: Loading a parser model/grammar text file (via readData during parser loading) whose options section has a line where the 'nPrune' field is expected but a different field appears — typically a stale or corrupted model file, or a file written by a different parser version.

Common situations: Mixing model files and library versions (e.g., loading a model trained with an older/newer Stanford Parser), manually edited grammar files, or truncated/mangled file transfers.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Expected blank line, found:
• format error in embeddings
• format error unexpected featureFactory line:
• expecting BEGIN block; got end of file.
• expecting BEGIN block; got

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/9219c4f65bc68810. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/parser/lexparser/Options.java:1265

    freeDependencies = Boolean.parseBoolean(value);
    line = in.readLine();
    value = line.substring(line.indexOf(' ') + 1);
    directional = Boolean.parseBoolean(value);
    line = in.readLine();
    value = line.substring(line.indexOf(' ') + 1);
    genStop = Boolean.parseBoolean(value);
    line = in.readLine();
    value = line.substring(line.indexOf(' ') + 1);
    distance = Boolean.parseBoolean(value);
    line = in.readLine();
    value = line.substring(line.indexOf(' ') + 1);
    coarseDistance = Boolean.parseBoolean(value);
    line = in.readLine();
    value = line.substring(line.indexOf(' ') + 1);
    dcTags = Boolean.parseBoolean(value);
    line = in.readLine();
    if ( ! line.matches("^nPrune.*")) {
      throw new RuntimeException("Expected nPrune, found: " + line);
    }
    value = line.substring(line.indexOf(' ') + 1);
    nodePrune = Boolean.parseBoolean(value);
    line = in.readLine(); // get rid of last line
    if (line.length() != 0) {
      throw new RuntimeException("Expected blank line, found: " + line);
    }
  }

  private static final long serialVersionUID = 4L;

} // end class Options

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