Must be lowercase – Elasticsearch Error How To Solve Related Issues

Must be lowercase – Elasticsearch Error How To Solve Related Issues

Updated: July-20

Elasticsearch 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 causing many errors 


This guide will help you check for common problems that cause the log “must be lowercase” 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: metadata, cluster.

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 discover the cause of many errors and provides suitable actionable recommendations (free tool that requires no installation). 

Log Context

Log”must be lowercase”classname  is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

* Validate the name for an index against some static rules and a cluster state.
  public void validateIndexName(String index; ClusterState state) {
  validateIndexOrAliasName(index; InvalidIndexNameException::new);
  if (!index.toLowerCase(Locale.ROOT).equals(index)) {
  throw new InvalidIndexNameException(index; "must be lowercase");
  // NOTE: dot-prefixed index names are validated after template application; not here
  if (state.routingTable().hasIndex(index)) {

Find Configuration Errors

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