stanfordnlp/CoreNLP · error · RuntimeIOException

ERROR: Incorrect format for the serialized coref graph

Error message

ERROR: Incorrect format for the serialized coref graph: ${line}

What it means

CustomAnnotationSerializer.read parses the old-format coref graph line as space-separated fields in groups of 4 (source tuple + destination tuple). If the number of fields is not a multiple of 4, the line cannot represent complete (src,dst) pairs and a RuntimeIOException is thrown.

Solutions

1. Regenerate the serialized annotation file with the same CoreNLP version used to read it
2. Check the coref line's field count is a multiple of 4 (sentIndex-copy pairs for src and dst)
3. Ensure the file transferred completely and was not truncated (compare checksums)
4. Use a consistent CustomAnnotationSerializer version for both write and read

Example fix

// before: truncated line with 6 fields (not multiple of 4)
// 0-1 0-2 1-0 1-1 2-0 2-1
// after: complete 4-field-group line
// 0-1 0-2 1-0 1-1

String[] bits = corefLine.split(" ");
if (bits.length % 4 != 0) throw new IllegalArgumentException("Coref line not multiple of 4 fields: " + corefLine);

static boolean hasCompleteCorefGroups(String line) {
  return line.trim().split(" ").length % 4 == 0;
}

try {
  Pair<Annotation, InputStream> p = serializer.read(in);
} catch (RuntimeIOException e) {
  if (e.getMessage().startsWith("ERROR: Incorrect format for the serialized coref graph")) {
    // re-transfer or regenerate the file
  } else throw e;
}

When it happens

Trigger: Reading a serialized annotation whose coref graph line has a field count not divisible by 4 — a truncated/corrupted file or one written by an incompatible serializer version.

Common situations: Loading annotations serialized with a different CoreNLP version whose coref format changed; incomplete file transfers; hand-edited coref lines dropping a field.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• ERROR: Invalid dependency node line
• ERROR: Invalid format for dependency graph
• ERROR: Invalid format token for serialized token
• RuntimeIOException wrapping IOException
• Failed to save classifier

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/9c9a0947098a5415. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/pipeline/CustomAnnotationSerializer.java:426

  }

  @Override
  public Pair<Annotation, InputStream> read(InputStream is) throws IOException {
    if(compress && !(is instanceof GZIPInputStream)) is = new GZIPInputStream(is);
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    Annotation doc = new Annotation("");
    String line;

    // read the coref graph (new format)
    Map<Integer, CorefChain> chains = loadCorefChains(reader);
    if(chains != null) doc.set(CorefCoreAnnotations.CorefChainAnnotation.class, chains);

    // read the coref graph (old format)
    line = reader.readLine().trim();
    if(line.length() > 0){
      String [] bits = line.split(" ");
      if(bits.length % 4 != 0){
        throw new RuntimeIOException("ERROR: Incorrect format for the serialized coref graph: " + line);
      }
      List<Pair<IntTuple, IntTuple>> corefGraph = new ArrayList<>();
      for(int i = 0; i < bits.length; i += 4){
        IntTuple src = new IntTuple(2);
        IntTuple dst = new IntTuple(2);
        src.set(0, Integer.parseInt(bits[i]));
        src.set(1, Integer.parseInt(bits[i + 1]));
        dst.set(0, Integer.parseInt(bits[i + 2]));
        dst.set(1, Integer.parseInt(bits[i + 3]));
        corefGraph.add(new Pair<>(src, dst));
      }
      doc.set(CorefCoreAnnotations.CorefGraphAnnotation.class, corefGraph);
    }

    // read individual sentences
    List<CoreMap> sentences = new ArrayList<>();
    while((line = reader.readLine()) != null){
      CoreMap sentence = new Annotation("");

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