diff --git a/limbo/testcases/online.py b/limbo/testcases/online.py
index 5958212d..9bef0fba 100644
--- a/limbo/testcases/online.py
+++ b/limbo/testcases/online.py
@@ -32,24 +32,35 @@
 ]
 
 
+def _peer_chain(*, host: str, port: int = 443, cafile: str = certifi.where()) -> list[Certificate]:
+    """
+    Returns the peer certificate and intermediate chain for a given TLS connection
+    on `(host, post)`.
+    """
+    ctx = SSL.Context(method=SSL.TLS_METHOD)
+    ctx.load_verify_locations(cafile=cafile)
+
+    conn = SSL.Connection(ctx, socket=socket.socket(socket.AF_INET, socket.SOCK_STREAM))
+    conn.set_tlsext_host_name(host.encode())
+    conn.connect((host, port))
+    conn.do_handshake()
+
+    chain = conn.get_verified_chain()
+    assert chain is not None
+
+    return [Certificate(c.to_cryptography()) for c in chain]
+
+
 def compile() -> None:
     # NOTE: Uses `ASSETS_DIR_RW` instead of `ASSETS_PATH` since the latter
     # is a read-only API for package resources.
     online_assets = ASSETS_DIR_RW / "online"
     online_assets.mkdir(exist_ok=True)
 
-    for site in _TOPSITES:
-        logger.info(f"generating online testcase for {site}")
-
-        ctx = SSL.Context(method=SSL.TLS_METHOD)
-        ctx.load_verify_locations(cafile=certifi.where())
-
-        conn = SSL.Connection(ctx, socket=socket.socket(socket.AF_INET, socket.SOCK_STREAM))
-        conn.set_tlsext_host_name(site.encode())
-        conn.connect((site, 443))
-        conn.do_handshake()
+    for host in _TOPSITES:
+        logger.info(f"generating online testcase for {host}")
 
-        peer_chain = [Certificate(c.to_cryptography()) for c in (conn.get_verified_chain() or [])]
+        peer_chain = _peer_chain(host=host)
 
         # NOTE: We use the peer certificate's own state to produce our expected
         #  validation time. This would be incorrect in a normal path validation operation,
@@ -61,25 +72,25 @@ def compile() -> None:
         ) + timedelta(seconds=1)
 
         builder = (
-            Builder(id=f"online::{site}", description=f"A valid chain for `{site}`.")
+            Builder(id=f"online::{host}", description=f"A valid chain for `{host}`.")
             .server_validation()
             .peer_certificate(peer_cert)
             .untrusted_intermediates(*peer_chain[1:-1])
             .trusted_certs(*peer_chain[-1:])
-            .expected_peer_name(PeerName(kind="DNS", value=site))
+            .expected_peer_name(PeerName(kind="DNS", value=host))
             .validation_time(peer_cert_validation_time)
             .succeeds()
         )
 
         testcase = builder.build()
-        path = online_assets / f"{site}.limbo.json"
-        path.write_text(testcase.json(indent=2))
+        path = online_assets / f"{host}.limbo.json"
+        path.write_text(testcase.model_dump_json(indent=2))
 
 
 def register_testcases() -> None:
     online_assets = ASSETS_PATH / "online"
     for tc_path in online_assets.iterdir():
-        testcase = Testcase.parse_raw(tc_path.read_text())
+        testcase = Testcase.model_validate_json(tc_path.read_text())
 
         print(f"loading pre-generated testcase: {testcase.id}")