@ad-freiburg/qlever

QLever.js

QLever is a fast SPARQL engine for knowledge graphs. This package contains QLever compiled to WebAssembly (via Emscripten), so you can build RDF indexes and run SPARQL queries directly in the browser or in Node.js, no server required.

Usage

QLever uses threads, so index building and querying are blocking calls. Run them inside a Web Worker (browser) or a worker thread (Node.js).

The package is an ES module; its default export is the module factory.

import factory from "@ad-freiburg/qlever";

const m = await factory();

// Put the input data into the in-memory filesystem.
m.FS.writeFile("/input.ttl", turtleData);

// Build an index.
const config = new m.IndexBuilderConfig();
config.baseName = "/index";
const file = new m.InputFileSpecification();
file.filename = "/input.ttl";
file.filetype = m.Filetype.Turtle;
const files = new m.InputFileSpecificationVector();
files.push_back(file);
config.inputFiles = files;
m.Qlever.buildIndex(config);

// Load the index and query it.
const engine = new m.Qlever(new m.EngineConfig(config));
const result = engine.query(
    "SELECT * WHERE { ?s ?p ?o }", m.MediaType.sparqlJson);
console.log(JSON.parse(result));

Browser deployment notes

• QLever uses pthreads and therefore SharedArrayBuffer. The page that loads the module must be cross-origin isolated, i.e. served with the headers Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp.
• Ship qlever.wasm alongside qlever.mjs. The loader resolves it relative to the module's own URL (import.meta.url), which bundlers like Vite and webpack handle automatically; point the locateFile module option at its location only if you deviate from that layout.
• The module is built for wasm64, which requires a recent browser (or Node.js ≥ 24).