When using the get_mappings tool, the server throws "Request failed (remote): error decoding response body" if a nested property is defined without explicitly specifying "type": "nested", even though the mapping is valid according to Elasticsearch specifications.

Example Mapping That Fails:

{ "mappings": { "properties": { "title": { "type": "text" }, "created_at": { "type": "date" }, "comments": { "properties": { "user": { "type": "keyword" }, "message": { "type": "text" }, "posted_at": { "type": "date" } } } } } }

Example mapping that works:

{ "mappings": { "properties": { "title": { "type": "text" }, "created_at": { "type": "date" }, "comments": { "type": "nested", "properties": { "user": { "type": "keyword" }, "message": { "type": "text" }, "posted_at": { "type": "date" } } } } } }

Difference: The working mapping includes "type": "nested" for the "comments" property.

The first mapping is valid and accepted by Elasticsearch, but the get_mappings tool fails to process it. This behavior is unexpected and may indicate a bug or an undocumented constraint in the tool’s handling of mappings.

Expected Behavior:
The tool should correctly decode and return mappings even when the "type": "nested" is omitted, as long as the mapping is valid per Elasticsearch standards.

Environment:
Elasticsearch version: 8.17.6
mcp-server-elasticsearch version: latest
Tool: get_mappings