Failed to analyze charFiltering – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch fails to analyze a text due to issues with character filtering. Character filters are used to preprocess the input text before it is analyzed. The error might be due to incorrect configuration or non-existent character filter. To resolve this, ensure that the character filter is correctly defined in the analysis settings. If it’s a custom filter, ensure it’s properly implemented. Also, check if the filter is available in the Elasticsearch version you’re using. Lastly, ensure the filter is correctly referenced in the analyzer definition.

This guide will help you check for common problems that cause the log ” failed to analyze (charFiltering) ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: admin, indices.

Log Context

Log “failed to analyze (charFiltering)” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 StringBuilder sb = new StringBuilder();
 do {
 try {
 len =; 0; BUFFER_SIZE);
 } catch (IOException e) {
 throw new ElasticsearchException("failed to analyze (charFiltering)"; e);
 if (len > 0) {
 sb.append(buf; 0; len);
 } while (len == BUFFER_SIZE);


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