Highlighting #

Ask for matched fragments of your text fields back alongside each hit, with the matched terms wrapped in tags — ready to render as a search result list.

POST /my-collection/_search

Example #

{
  "query": { "match": { "field": "message", "query": "search" } },
  "highlight": {
    "fields": {
      "message": {
        "fragment_size": 100,
        "number_of_fragments": 3
      }
    }
  },
  "size": 5
}

Each returned hit carries a highlight object whose keys are the requested fields; values are fragment strings with matched terms wrapped in the tags (default <em> … </em>). Custom tags — same idea with <b> wrapping:

Parameters #

Top level:

• fields
  (Required, object) Map of field name (or "*" for every text field in the schema that the query touched) to per-field options below.
• pre_tags
  (Optional, array of strings, default: ["<em>"]) Tag(s) emitted before a matched term.
• post_tags
  (Optional, array of strings, default: ["</em>"]) Tag(s) emitted after a matched term.

Per field:

• fragment_size
  (Optional, integer, default: 100) Target length of each fragment in characters. 0 returns the whole field value instead of fragments.
• number_of_fragments
  (Optional, integer, default: 5) Maximum fragments returned per field. 0 returns the whole field.
• no_match_size
  (Optional, integer) When the document has the field but nothing matched, return this many characters from the start of the value instead of nothing.

Notes #

• Highlighting uses the same analyzer as the field, so phrase and span matches highlight the same terms the query scored.
• Fragments are selected around the densest cluster of matches, best first.
• Combine with fields/_source filtering to return highlights without the full source when bandwidth matters.