Failed to analyze charFiltering – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

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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.

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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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