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USearch

Unum
open source / Overall score: 3.0

USearch is a single-file similarity search and clustering engine implementing HNSW over user-defined metrics, including spatial, binary and probabilistic distances. The C++ header compiles into bindings for a dozen languages and runs on desktop, mobile, WebAssembly and inside SQLite. Unum develops it.

Openness

5 high confidence
5.0
license
Apache-2.0(OSI)
source
public
core features withheld
no

Apache-2.0 license body confirmed. The repository is public and unarchived and builds the whole product, and the README describes no paid tier, enterprise edition or license-gated build beside it, so source is public and the core ungated.

Adoption

3 high confidence
3.0

USearch's adoption reading comes directly from PyPI downloads of the package, since the library itself is the distributed artifact rather than a client for a separate service. That is a direct signal of use, though it counts only PyPI installs and not use through the other eleven language bindings.

Capability

3 medium confidence
3.0

USearch provides one index family, HNSW, with pluggable metrics and quantized vector types, embeddable across a dozen language bindings and four platform classes rather than any broader set of retrieval modes. That narrow focus is why it covers much less of the persist-index-retrieve path than Vespa's distributed, cluster-capable platform.

Verified 2026-09-24