stanfordnlp/CoreNLP · error · RuntimeException

Cannot find matching labelled span for

Error message

Cannot find matching labelled span for 

What it means

getLabelledSpans builds spans from bracket-style CoNLL labels (e.g. coref and NER columns). While scanning a token's label set against the currently open spans, a close marker arrived whose label does not match any open span, and openSpans ran out without finding a match. This means the bracket annotations in the corpus column are unbalanced or mismatched, so the library throws a RuntimeException.

Solutions

1. Validate the annotation file: every opening label like (LABEL must have a matching closing LABEL) in the same column
2. Regenerate the file from the original CoNLL-2012 distribution rather than hand-editing
3. Check that your preprocessing did not merge or reorder tokens within a sentence, breaking bracket pairing
4. Log the sentence and column (concatField) at failure to locate the offending line before fixing it

Example fix

// before (hand-edited line)
 token (ARG0)
 token )
 token ARG0)   <- closing without open
// after
 token (ARG0
 token ARG0)    <- balanced brackets in the coref column

// Pre-check a coref/NER column for balanced brackets
static boolean bracketsBalanced(String col) { int opens=0; for (String tok : col.split("\\s+")) { for (String part : tok.split("(?=\\()|(?<=\\))")) { if (part.startsWith("(")) opens++; if (part.endsWith("))")) opens-=2; else if (part.endsWith(")")) opens--; if (opens<0) return false; } } return opens==0; }

try { spans = reader.getLabelledSpans(...); } catch (RuntimeException e) { if (e.getMessage().startsWith("Cannot find matching labelled span")) { throw new CorruptAnnotationException(e.getMessage() + " — fix brackets in the column", e); } throw e; }

When it happens

Trigger: A token carries a closing label (or an Openify/Closeify mismatch) such that popping openSpans never yields the expected label s; i.e. malformed coref or NER bracket encoding in a line of the CoNLL file.

Common situations: Hand-edited or truncated CoNLL files where an opening bracket was deleted; column-shifting edits (tabs/space changed) so labels are read from the wrong column; custom-preprocessed corpora that closed spans out of order.

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 extracting labelled spans for column :
• Unexpected number of field , expected >= for line (,):
• INVALID LINE: "${line}"
• ERROR: Invalid dependency node line: ${line}
• ERROR: Invalid format for dependency graph: ${line}

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/57ca0615306e13e0. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/coref/docreader/CoNLLDocumentReader.java:426

                openParenIndex = -1;
              }
              isDelimiter = true;
            }
            if (c == '(') {
              openParenIndex = j;
            } else if (c == ')') {
              Triple<Integer, Integer, String> t = openSpans.pop();
              if (checkEndLabel) {
                // NOTE: end parens may cross (usually because mention either start or end on the same token
                // and it is just an artifact of the ordering
                String s = val.substring(lastDelimiterIndex+1, j);
                if (!s.equals(t.third())) {
                  Stack<Triple<Integer,Integer, String>> saved = new Stack<>();
                  while (!s.equals(t.third())) {
                    // find correct match
                    saved.push(t);
                    if (openSpans.isEmpty()) {
                      throw new RuntimeException("Cannot find matching labelled span for " + s);
                    }
                    t = openSpans.pop();
                  }
                  while (!saved.isEmpty()) {
                    openSpans.push(saved.pop());
                  }
                  assert(s.equals(t.third()));
                }
              }
              t.setSecond(wordPos);
              spans.add(t);
            }
            if (isDelimiter) {
              lastDelimiterIndex = j;
            }
          }
          if (openParenIndex >= 0) {
            String s = val.substring(openParenIndex+1, val.length());

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