diff --git a/axon/services/quality.py b/axon/services/quality.py
new file mode 100644
index 0000000..20f9d48
--- /dev/null
+++ b/axon/services/quality.py
@@ -0,0 +1,27 @@
+from urllib.parse import urlparse
+
+from axon.models import SearchResult
+
+_HIGH_TRUST_TLDS = {".gov", ".edu"}
+_KNOWN_HIGH_TRUST = {"wikipedia.org", "github.com", "arxiv.org", "nature.com", "who.int"}
+
+
+def score_source(result: SearchResult) -> float:
+    parsed = urlparse(result.url)
+    host = (parsed.hostname or "").lower().removeprefix("www.")
+    score = 0.5
+    if any(host.endswith(tld) for tld in _HIGH_TRUST_TLDS):
+        score += 0.25
+    if any(host == domain or host.endswith(f".{domain}") for domain in _KNOWN_HIGH_TRUST):
+        score += 0.2
+    if result.published_date:
+        score += 0.05
+    if len(result.content) > 200:
+        score += 0.05
+    return round(min(score, 1.0), 3)
+
+
+def annotate_source_quality(results: list[SearchResult]) -> list[SearchResult]:
+    for result in results:
+        result.source_quality = score_source(result)
+    return results