Illegal type for _source: – How to solve this Elasticsearch error

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Illegal type for _source: – How to solve this Elasticsearch error

Opster Team

July-20, Version: 1.7-8.0

Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which can resolve issues that cause many errors.

This guide will help you check for common problems that cause the log ” illegal type for _source: ” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: Node.

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to pinpoint the cause of many errors and provides suitable actionable recommendations how to resolve them (free tool that requires no installation).

Log Context

Log”illegal type for _source: [{}]”classname  is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

  } else if (token == Token.VALUE_STRING) {
  fetchSourceContext = new FetchSourceContext(fetchSourceContext.fetchSource();
  new String[]{parser.text()}; fetchSourceContext.excludes());
  } else {
  throw new ElasticsearchParseException("illegal type for _source: [{}]"; token);
  } else {
  throw new ElasticsearchParseException("failed to parse multi get request. unknown field [{}]"; currentFieldName);
  } else if (token == Token.START_ARRAY) {


Run the Check-Up to get a customized report like this:

Analyze your cluster