diff --git a/swh/graph/server/app.py b/swh/graph/server/app.py
--- a/swh/graph/server/app.py
+++ b/swh/graph/server/app.py
@@ -22,9 +22,14 @@
     from async_generator import asynccontextmanager  # type: ignore
 
 
+# content-type for NDJSON, see http://ndjson.org/
+NDJSON_CT = 'application/x-ndjson'
+
+
 @asynccontextmanager
-async def stream_response(request, *args, **kwargs):
+async def stream_response(request, content_type='text/plain', *args, **kwargs):
     response = aiohttp.web.StreamResponse(*args, **kwargs)
+    response.content_type = content_type
     await response.prepare(request)
     yield response
     await response.write_eof()
@@ -101,7 +106,7 @@
 
     src_node = backend.pid2node[src]
     it = backend.visit_paths(direction, edges, src_node)
-    async with stream_response(request) as response:
+    async with stream_response(request, content_type=NDJSON_CT) as response:
         async for res_path in it:
             res_path_pid = [backend.node2pid[n] for n in res_path]
             line = json.dumps(res_path_pid)
@@ -121,8 +126,7 @@
         src_node = backend.pid2node[src]
         cnt = await loop.run_in_executor(
             None, backend.count, ttype, direction, edges, src_node)
-        return aiohttp.web.Response(body=str(cnt),
-                                    content_type='application/json')
+        return aiohttp.web.Response(body=str(cnt), content_type='text/plain')
 
     return count