Parsing of sentence failed, possibly because of out of…

Error message

Parsing of sentence failed, possibly because of out of memory.  Will ignore and continue: ${words}

What it means

ParserAnnotator catches NoSuchParseException during doOneSentence and logs this warning instead of propagating. The parse of the sentence failed, likely because the parser exhausted memory while parsing; the sentence is skipped and annotation continues. This is a resilience mechanism so one bad sentence does not abort an entire document.

Solutions

Increase JVM heap: java -Xmx4g (or more) when running the pipeline
Set -parse.maxlen (e.g. 100) so overly long sentences are skipped before the parser attempts them
Split very long sentences during preprocessing (split on semicolons/newlines)
Log the sentence text and exclude/retry it individually to isolate the offender
Reduce kBest (k-best parse count) if you configured a large value

Example fix

// before
java -cp stanford-corenlp.jar edu.stanford.nlp.pipeline.StanfordCoreNLP -annotators tokenize,ssplit,parse -file input.txt
// after
java -Xmx8g -cp stanford-corenlp.jar edu.stanford.nlp.pipeline.StanfordCoreNLP -annotators tokenize,ssplit,parse -parse.maxlen 100 -file input.txt

Defensive patterns

Strategy: try-catch

Validate before calling

if (sentence.split("\\s+").length > maxSentenceLength) {
  throw new IllegalArgumentException("Sentence too long for parser: " + sentence.length());
}

Try / catch

try {
  pipeline.annotate(annotation);
} catch (Throwable t) {
  if (t instanceof OutOfMemoryError) {
    log.warn("Parser ran out of memory on sentence; skipping");
  } else {
    throw t;
  }
}

Prevention

Run the JVM with generous -Xmx heap
Set -parse.maxlen to skip overly long sentences
Pre-split long sentences in preprocessing
Monitor memory when batch-annotating large corpora

When it happens

Trigger: Annotating a document with the 'parse' annotator when one sentence is so syntactically complex/long that the probabilistic parser (Levin/lexparser) throws NoSuchParseException, commonly under heap pressure.

Common situations: Processing long sentences from legal/academic text with default heap; running CoreNLP in memory-constrained containers; batch-annotating large corpora where one sentence blows the stack/heap.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/1bfb6b2b6801f024. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/pipeline/ParserAnnotator.java:370

        if (scoredObjects == null || scoredObjects.size() < 1) {
          log.warn("Parsing of sentence failed.  " +
              "Will ignore and continue: " +
              SentenceUtils.listToString(words));
        } else {
          for (ScoredObject<Tree> so : scoredObjects) {
            // -10000 denotes unknown words
            Tree tree = so.object();
            tree.setScore(so.score() % -10000.0);
            trees.add(tree);
          }
        }
      }
    } catch (OutOfMemoryError e) {
      log.error(e); // Beware that we can now get an OOM in logging, too.
      log.warn("Parsing of sentence ran out of memory (length=" + words.size() + ").  " +
              "Will ignore and try to continue.");
    } catch (NoSuchParseException e) {
      log.warn("Parsing of sentence failed, possibly because of out of memory.  " +
              "Will ignore and continue: " +
              SentenceUtils.listToString(words));
    }
    return trees;
  }

  @Override
  public Set<Class<? extends CoreAnnotation>> requires() {
    if (parser.requiresTags()) {
      return Collections.unmodifiableSet(new ArraySet<>(Arrays.asList(
          CoreAnnotations.TextAnnotation.class,
          CoreAnnotations.TokensAnnotation.class,
          CoreAnnotations.ValueAnnotation.class,
          CoreAnnotations.OriginalTextAnnotation.class,
          CoreAnnotations.CharacterOffsetBeginAnnotation.class,
          CoreAnnotations.CharacterOffsetEndAnnotation.class,
          CoreAnnotations.IndexAnnotation.class,
          CoreAnnotations.SentencesAnnotation.class,

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