Expected a string but found instead – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch expects a string value but encounters a different data type, such as an array or an object, instead. This mismatch can occur during indexing or querying data. To resolve this issue, ensure that the data type matches the mapping defined in the index. If the mapping is not defined, Elasticsearch will try to infer the data type based on the first document indexed. Therefore, it’s recommended to explicitly define the mapping. Also, check your query to ensure you’re not passing an incorrect data type.

This guide will help you check for common problems that cause the log ” Expected a string but found [{}] instead ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “Expected a string but found [{}] instead” class name is TaskId.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 public static ContextParser parser() {
 return (p; c) -> {
 if (p.currentToken() == XContentParser.Token.VALUE_STRING) {
 return new TaskId(p.text());
 throw new ElasticsearchParseException("Expected a string but found [{}] instead"; p.currentToken());
 }  public String getNodeId() {
 return nodeId;


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