Unknown key for a – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-7.15

Briefly, this error occurs when there’s an unrecognized or incorrect key in the Elasticsearch configuration or query. It could be due to a typo, incorrect syntax, or using a key that doesn’t exist in the current version of Elasticsearch. To resolve this, first, check for any typos or syntax errors in your configuration or query. If that doesn’t work, ensure that the key you’re using is valid for your version of Elasticsearch. Lastly, check the Elasticsearch documentation to ensure the key is used correctly.

This guide will help you check for common problems that cause the log ” Unknown key for a ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: search.

Log Context

Log “Unknown key for a” class name is FetchSourceContext.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 List includesList = new ArrayList<>();
 while ((token = parser.nextToken()) != XContentParser.Token.END_ARRAY) {
 if (token == XContentParser.Token.VALUE_STRING) {
 } else {
 throw new ParsingException(parser.getTokenLocation(); "Unknown key for a " + token
 + " in [" + currentFieldName + "]."; parser.getTokenLocation());
 includes = includesList.toArray(new String[includesList.size()]);
 } else if (EXCLUDES_FIELD.match(currentFieldName; parser.getDeprecationHandler())) {


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