diff --git a/src/rerank.rs b/src/rerank.rs
index 4b0fd9d..7773132 100644
--- a/src/rerank.rs
+++ b/src/rerank.rs
@@ -1 +1,26 @@
-// implemented in a later task
+use crate::ionos::IonosClient;
+use crate::model::AppError;
+
+/// Cross-encoder rerank. Returns a score per document, aligned to the
+/// input `docs` order (results are re-sorted back by their index).
+pub fn rerank(
+    client: &IonosClient, model: &str, query: &str, docs: &[String],
+) -> Result<Vec<f32>, AppError> {
+    if docs.is_empty() { return Ok(vec![]); }
+    let body = serde_json::json!({
+        "model": model, "query": query, "documents": docs
+    });
+    let resp: serde_json::Value = client.post_json("/rerank", &body)?;
+    let results = resp["results"].as_array()
+        .ok_or_else(|| AppError::Ionos("rerank: no results[]".into()))?;
+    let mut scores = vec![0.0f32; docs.len()];
+    for r in results {
+        let idx = r["index"].as_u64().ok_or_else(
+            || AppError::Ionos("rerank: no index".into()))? as usize;
+        let sc = r["relevance_score"].as_f64()
+            .or_else(|| r["score"].as_f64())
+            .ok_or_else(|| AppError::Ionos("rerank: no score".into()))? as f32;
+        if idx < scores.len() { scores[idx] = sc; }
+    }
+    Ok(scores)
+}
diff --git a/tests/rerank_tests.rs b/tests/rerank_tests.rs
new file mode 100644
index 0000000..f26ac2d
--- /dev/null
+++ b/tests/rerank_tests.rs
@@ -0,0 +1,24 @@
+use alpha_id::rerank::rerank;
+use alpha_id::ionos::IonosClient;
+use std::io::Write;
+
+#[test]
+fn rerank_returns_scores_aligned_to_documents() {
+    let server = tiny_http::Server::http("127.0.0.1:0").unwrap();
+    let url = format!("http://{}", server.server_addr());
+    let h = std::thread::spawn(move || {
+        if let Ok(req) = server.recv() {
+            let body = r#"{"results":[{"index":0,"relevance_score":0.2},
+                                       {"index":1,"relevance_score":0.9}]}"#;
+            req.respond(tiny_http::Response::from_string(body)).ok();
+        }
+    });
+    let mut tf = tempfile::NamedTempFile::new().unwrap();
+    write!(tf, "tok").unwrap();
+    let c = IonosClient::new(&url, tf.path().to_str().unwrap()).unwrap();
+    let scores = rerank(&c, "Qwen/Qwen3-VL-Reranker-8B", "diabetes",
+                        &["herzinfarkt".to_string(), "diabetes typ 2".to_string()]).unwrap();
+    assert_eq!(scores.len(), 2);
+    assert!(scores[1] > scores[0]);
+    h.join().ok();
+}