What is Inverted index?
Verified 5 August 2026
Rather than scanning documents for terms, an inverted index stores, for every term, a posting list of the documents containing it and where. A query intersects or unions the relevant posting lists, touching only documents that contain the query terms.
Posting lists compress well and page from disk efficiently, which means the lexical tier of a search engine need not be resident in memory to be fast.
Common questions
What is Inverted index?
An inverted index maps each term to the list of documents containing it, which is what makes lexical search fast.
How does Inverted index work in practice?
Posting lists compress well and page from disk efficiently, which means the lexical tier of a search engine need not be resident in memory to be fast.
See it working
The free tier is 10,000 requests a month with no card — enough to test any of this against your own queries.