Index independence
Index independence is whether a search engine answers queries from a web index it crawled and built itself or passes them to another engine’s index. An independent engine has its own crawler, index and ranking, while many search APIs resell or re-rank results from a larger engine. Independence affects coverage, pricing and supply risk: when an upstream index changes its terms, every engine built on it is affected.
The question became practical when Microsoft retired the Bing Search APIs on August 11, 2025, and products built on them had to find another source. Benchmarks can estimate independence from outside by measuring how often two engines return the same URLs for the same queries.
Example
Two search APIs return the same three low-quality pages for a rare query. A single case can be chance. If the pattern repeats across hundreds of queries, the two APIs most likely read from the same upstream index.
How it works in NEEDLE
NEEDLE estimates index independence with an overlap matrix for every pair of engines. A pair counts as sharing suspiciously on a query when both return at least one URL the judge rated below Highly Meets, or at least three of the same URLs. Sharing good results is normal ranking behavior. Repeatedly sharing weak results suggests that two engines use the same upstream index. See the live NEEDLE overlap matrix.
FAQ
Why does index independence matter for AI agents?
An agent built on a search API inherits that API’s coverage and its supplier. When the API runs its own index, a change in another company’s terms or prices does not change the agent’s results or costs overnight.
How can you check whether two search APIs share an index?
Send both APIs the same set of queries and compare the URLs they return. Occasional overlap on good pages is normal. Repeated overlap on the same weak pages suggests that both read from one index.
Related terms
Written by Keenable.
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