elastic/elasticsearch · error · IllegalArgumentException

length parameter must be provided

Error message

length parameter must be provided

What it means

The truncate token filter requires a positive integer length. The constructor reads settings.getAsInt("length", -1) and rejects any value <= 0. Because the default is -1, simply omitting the key is sufficient to trip the check, as is explicitly passing 0 or a negative number.

Source

Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/TruncateTokenFilterFactory.java:27

package org.elasticsearch.analysis.common;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.miscellaneous.TruncateTokenFilter;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.env.Environment;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.analysis.AbstractTokenFilterFactory;

public class TruncateTokenFilterFactory extends AbstractTokenFilterFactory {

    private final int length;

    TruncateTokenFilterFactory(IndexSettings indexSettings, Environment environment, String name, Settings settings) {
        super(name);
        this.length = settings.getAsInt("length", -1);
        if (length <= 0) {
            throw new IllegalArgumentException("length parameter must be provided");
        }
    }

    @Override
    public TokenStream create(TokenStream tokenStream) {
        return new TruncateTokenFilter(tokenStream, length);
    }
}

View on GitHub (pinned to db6a809a66)

Solutions

1. Add "length": N with N >= 1 (it is the maximum token length in characters; tokens longer than N are truncated to N).
2. Verify the key is spelled exactly 'length' and lives inside the filter object.
3. If you want no truncation, remove the filter entirely instead of passing 0.

Example fix

// before
"filter": { "my_trunc": { "type": "truncate" } }
// after
"filter": { "my_trunc": { "type": "truncate", "length": 10 } }

// Require a positive length on every truncate filter
static String checkTruncate(Map<String,Object> filter) {
  if ("truncate".equals(filter.get("type"))) {
    Object len = filter.get("length");
    if (!(len instanceof Number) || ((Number) len).intValue() <= 0)
      return "truncate filter requires length > 0";
  }
  return null;
}

When it happens

Trigger: Creating an analyzer whose filter is type 'truncate' without a 'length' key, or with length <= 0.

Common situations: Copying a truncate example that omitted length; mistyping the key as 'max' or 'size'; intending 'no truncation' and passing 0.

Related errors

• classname is a required setting for esplugin
• classname is a forbidden for stable esplugin
• invalid deploymentTarget '{}', expected one of {}
• Number of nodes should be >= 1 but was {} for {}
• Cannot shrink {} to have {} nodes as it already has {}

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/2b06724b242bd342. Report an issue: GitHub.