elastic/elasticsearch · error · IllegalArgumentException

Token filter [{}] cannot be used to parse synonyms

Error message

Token filter [{}] cannot be used to parse synonyms

What it means

Error "Token filter [{}] cannot be used to parse synonyms" thrown in elastic/elasticsearch.

Source

Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/EdgeNGramTokenFilterFactory.java:86

        result = new EdgeNGramTokenFilter(result, minGram, maxGram, preserveOriginal);

        // side=BACK is not supported anymore but applying ReverseStringFilter up-front and after the token filter has the same effect
        if (side == SIDE_BACK) {
            result = new ReverseStringFilter(result);
        }

        return result;
    }

    @Override
    public boolean breaksFastVectorHighlighter() {
        return true;
    }

    @Override
    public TokenFilterFactory getSynonymFilter() {
        throw new IllegalArgumentException("Token filter [" + name() + "] cannot be used to parse synonyms");
    }
}

View on GitHub (pinned to db6a809a66)

When it happens

Trigger: Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/EdgeNGramTokenFilterFactory.java:86 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/ab73a709e8a69956. Report an issue: GitHub.