Search engines built for a single content type or professional domain rather than general web search — typically indexing a specific, structured corpus that general-purpose engines cover poorly or not at all.
What unites this category is depth over breadth: each engine below indexes a narrower body of content than Google or Bing, but does so with domain-specific structure, filtering, and ranking that a general web index typically cannot replicate for that use case.
A vertical search engine indexing academic papers, theses, books, and case law, including citation counts and "cited by" tracking, widely used for scholarly research and legal citation analysis.
The U.S. National Library of Medicine's search engine for biomedical and life sciences literature, a primary and heavily cited source for medical and clinical research.
A "computational knowledge engine" that computes answers directly from structured, curated data rather than retrieving and ranking existing documents, geared primarily toward mathematical, scientific, and factual queries.
A vertical search engine aggregating job listings scraped and syndicated from company career pages and other job boards across the web, functioning as a search layer over the fragmented job-posting landscape.
A code search engine built for searching across source code repositories at scale, supporting the kind of structural and syntax-aware queries that a general-purpose engine's text index isn't built to handle.