This section lists modules that add new backends, plugins or other extensions to the Search API, allowing users to add additional functionality to their sites. Creators of new extension modules are welcome to add their projects to this list, too.

This page also acts as the parent for documentation on those extension modules.

Modules providing service classes

Solr search (7.x, 8.x)
A backend using an Apache Solr server for indexing and searching, like the popular Apache Solr Search Integration module. It uses dynamic fields for indexing arbitrary entities and boasts far superior indexing- and search-performance, better result accuracy and native facetting support.
Multilingual Solr search (8.x)
An extension of the Solr search backend. It provides sensible default settings for different languages and hides the complexity of defining per language filed types within a Solr schema. Additionally, a lot of fine-tuning of the index could be done within Drupal instead of editing Solr config files manually.
Database search (7.x, 8.x is internal module of search_api module)
A simple, database-based backend for indexing and searching data. It's neither very fast nor accurate, but it works out of the box and can be used for testing out the Search API capabilities (it even supports facetting), or for smaller sites (or smaller, less important indexes/searches).
Fuzzy Search (7.x)
A more advanced database-based backend which also allows fuzzy matches and substring matching. No longer maintained.
Xapian (7.x)
The xapian project now includes a separate module, search_api_xapian, that provides a Xapian backend for the Search API. Facets currently aren't supported yet, but planned for the future (as of January 2011).
Sarnia (7.x)
Sarnia is an extension of the Solr search module which provides the capability to search and display non-Drupal data indexed in Solr.
Mongo DB backend (7.x)
Uses a Mongo DB for indexing and searching. Fast and scalable, it's a great alternative to the normal database backend.
Sphinx (7.x)
Uses Sphinx for indexing and searching. Supports several features, including facets and "More Like This".
Elasticsearch (7.x)
Uses Elasticsearch for indexing, analysis, and searching. Facets, autocomplete, and "more like this" are currently supported features with new features being added on a regular basis. This module uses the Elastica PHP client library.
Elasticsearch Connector (7.x, 8.x)
Elasticsearch Connector is a set of modules designed to build a full Elasticsearch eco system in Drupal. This module uses the official Elasticsearch PHP library. The ambitions of this module are to help Drupal handle big data at any kind and make it scalable.
Search API Algolia (7.x, 8.x)
Search API Algolia enables site builders to push content into Algolia's cloud. It provides out of the box indexing capabilities of Drupal entities (nodes, taxonomy terms, users, etc...). The actual search interface has to be provided separately (Algolia's demos can provide some useful implementation pointers).
Xunsearch (7.x, 8.x)
Xunsearch is a variants based on xapian, with comprehensive chinese support via scws, which is a tokenlizer for chinese.
Currently both 7.x and 8.x modules are provided.
Search API OpenSearch
Search API OpenSearch provides a backend for OpenSearch using the official OpenSearch PHP Client. Provides indexing, field mapping, views, more like this, and facets.
Typesense
The module provides a backend for Typesense. Currently, it implements enough of the Search API api to enable it to be used in semi-decoupled projects--e.g. where a javascript app provides the whole ux from the search form to pagination.
Search API Meilisearch
Search API Meilisearch provides a backend for Meilisearch using the official Meilisearch PHP Client. Provides indexing, filtering & sorting, synonyms, stopwords, facets*, and autocomplete* (*using submodules).

Other extension modules

Flag Search API (8.x)
Lets users index flags using Search API and use them in Views for example.
Search pages (7.x, 8.x)
A module for creating simple search pages, not using Views or any other modules. They can be used when a view would be unnecessarily slow, or for quickly testing out functionality. They also provide search blocks for starting a search from anywhere on the site.
Multi-index searches (7.x, no need for 8.x)
An extension for executing a search query on several indexes at once, for servers supporting that feature (like servers with the Solr backend).
Saved searches (7.x)
Lets users create search notifications so they are notified when new results are available.
Autocomplete (7.x, 8.x)
Allows to add dynamic autocompletion to fulltext key fields on search forms.
Google Analytics Search API Autocomplete (8.x)
Integrates Autocomplete widgets with Google Analytics.
Search API attachments (7.x, 8.x)
An extension that helps to allow indexing of attachment (or other file) contents.
The extraction can be done using :
Apache Tika Library
or
The Solr built-in extractor since version 1.3.
or
Acquia Search since version 1.4.
Extended search page (7.x)
This module provides a page like the default "Find content" page, but based on the Search API and therefore more flexible and richer in features.
Facet API Pretty Paths (7.x)
Enables pretty paths for searches with Facet API, which is often used in combination with Search API.
Search API Exclude Entity (8.x)
This module is the Drupal 8 / Search API successor to Apache Solr Node Exclude (7.x).
It makes it possible to exclude nodes and other entities from being indexed in
search indexed configured using Search API framework.
Search API ranges (7.x)
Adds the ability to add range facets for numeric fields to searches, with a nice ruler UI.
Search API sorts (7.x, 8.x)
Offers highly configurable sort blocks for all searches.
Search API context (7.x)
Provides "context-sensitive" blocks for Search API.
Search API AJAX (7.x)
Provides base functionality for AJAXifying search pages.
Search API Location (7.x, 8.x)
Allows indexing and searching of geolocation data with the Solr backend.
Search API live results (7.x)
Alternative to Autocomplete that shows potential results while typing.
Search API Entity Translation (7.x)
Search API Entity Translation allows you to index items in several languages when using Entity translation, as well as offering a few other tools for multilingual sites.
Search API Override (7.x)
This module allows you to override Search API server settings from within settings.php – the prime use being to override servers stored in features on development and staging servers.
Search API Spellcheck (7.x, 8.x)
Provides a "Did you mean.. [spelling]" option on search results.
Search API stats (7.x)
This module provides a "Top searches" block displaying popular search terms.
Search API Synonym (8.x)
Managing of synonyms and spelling errors from Drupal. Synonym files can be exported with Drupal Console and deployed to Solr or another search backend.
Search API Best Bets (8.x)
Managing of best bets directly in Drupal and integration to Solr using elevateIds and exlcudeIds search query parameters.