diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,4 +9,5 @@
 numpy
 dash
 dash_bootstrap_components
+flask
 dulwich
diff --git a/swh/scanner/backend.py b/swh/scanner/backend.py
new file mode 100644
--- /dev/null
+++ b/swh/scanner/backend.py
@@ -0,0 +1,41 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from flask import Flask, request
+
+from .db import Db
+from .exceptions import LargePayloadExc
+
+LIMIT = 1000
+
+
+def create_app(db: Db):
+    """Backend for swh-scanner, implementing the /known endpoint of the
+       Software Heritage Web API"""
+    app = Flask(__name__)
+
+    @app.route("/api/1/known/", methods=["POST"])
+    def known():
+        swhids = request.get_json()
+
+        if len(swhids) > LIMIT:
+            raise LargePayloadExc(
+                f"The maximum number of SWHIDs this endpoint can receive is {LIMIT}"
+            )
+
+        cur = db.conn.cursor()
+        res = {swhid: {"known": db.known(swhid, cur)} for swhid in swhids}
+        cur.close()
+
+        return res
+
+    return app
+
+
+def run(host: str, port: int, db: Db):
+    """Serve the local database
+    """
+    app = create_app(db)
+    app.run(host, port, debug=True)
diff --git a/swh/scanner/cli.py b/swh/scanner/cli.py
--- a/swh/scanner/cli.py
+++ b/swh/scanner/cli.py
@@ -18,6 +18,9 @@
 
 from .exceptions import DBError
 
+# Config for the "serve" option
+BACKEND_DEFAULT_PORT = 5011
+
 # All generic config code should reside in swh.core.config
 CONFIG_ENVVAR = "SWH_CONFIG_FILE"
 DEFAULT_CONFIG_PATH = os.path.join(click.get_app_dir("swh"), "global.yml")
@@ -191,6 +194,46 @@
         sys.exit(1)
 
 
+@db.command("serve")
+@click.option(
+    "-h",
+    "--host",
+    metavar="HOST",
+    default="127.0.0.1",
+    show_default=True,
+    help="The host of the API server",
+)
+@click.option(
+    "-p",
+    "--port",
+    metavar="PORT",
+    default=f"{BACKEND_DEFAULT_PORT}",
+    show_default=True,
+    help="The port of the API server",
+)
+@click.option(
+    "-f",
+    "--db-file",
+    "db_file",
+    metavar="DB_FILE",
+    default="SWHID_DB.sqlite",
+    show_default=True,
+    type=click.Path(exists=True),
+    help="An sqlite database file (it can be generated with: 'swh scanner db import')",
+)
+@click.pass_context
+def serve(ctx, host, port, db_file):
+    """Start an API service using the sqlite database generated with the "db import"
+    option."""
+    import swh.scanner.backend as backend
+
+    from .db import Db
+
+    db = Db(db_file)
+    backend.run(host, port, db)
+    db.close()
+
+
 def main():
     return scanner(auto_envvar_prefix="SWH_SCANNER")
 
diff --git a/swh/scanner/db.py b/swh/scanner/db.py
--- a/swh/scanner/db.py
+++ b/swh/scanner/db.py
@@ -64,6 +64,5 @@
         """Check if a given SWHID is present or not inside the local database."""
         cur.execute("""SELECT 1 FROM swhids WHERE swhid=?""", (swhid,))
         res = cur.fetchone()
-        cur.close()
 
         return res is not None
diff --git a/swh/scanner/exceptions.py b/swh/scanner/exceptions.py
--- a/swh/scanner/exceptions.py
+++ b/swh/scanner/exceptions.py
@@ -12,6 +12,10 @@
     pass
 
 
+class LargePayloadExc(Exception):
+    pass
+
+
 class DBError(Exception):
     pass
 
diff --git a/swh/scanner/tests/test_backend.py b/swh/scanner/tests/test_backend.py
new file mode 100644
--- /dev/null
+++ b/swh/scanner/tests/test_backend.py
@@ -0,0 +1,61 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.scanner.backend import LIMIT, create_app
+from swh.scanner.db import Db
+
+from .data import present_swhids
+
+
+def test_backend_endpoint_all_present(tmp_path, live_server, test_swhids_sample):
+    tmp_dbfile = tmp_path / "tmp_db.sqlite"
+    db = Db(tmp_dbfile)
+    cur = db.conn.cursor()
+    db.create_from(test_swhids_sample, LIMIT, cur)
+
+    app = create_app(db)
+
+    with app.test_client() as test_client:
+        res = test_client.post("/api/1/known/", json=present_swhids)
+
+        for swhid, attr in res.json.items():
+            assert attr["known"]
+
+
+def test_backend_endpoint_one_not_present(tmp_path, live_server, test_swhids_sample):
+    tmp_dbfile = tmp_path / "tmp_db.sqlite"
+    not_present_swhid = "swh:1:cnt:fa8eacf43d8646129ae8adfa1648f9307d999999"
+    swhids = present_swhids + [not_present_swhid]
+
+    db = Db(tmp_dbfile)
+    cur = db.conn.cursor()
+    db.create_from(test_swhids_sample, LIMIT, cur)
+
+    app = create_app(db)
+
+    with app.test_client() as test_client:
+        res = test_client.post("/api/1/known/", json=swhids)
+
+        for swhid, attr in res.json.items():
+            if swhid != not_present_swhid:
+                assert attr["known"]
+            else:
+                assert not attr["known"]
+
+
+def test_backend_large_payload_exc(tmp_path, live_server, test_swhids_sample):
+    tmp_dbfile = tmp_path / "tmp_db.sqlite"
+    swhid = "swh:1:cnt:fa8eacf43d8646129ae8adfa1648f9307d999999"
+    # the backend supports up to 1000 SWHID requests
+    swhids = [swhid for n in range(1001)]
+    db = Db(tmp_dbfile)
+    cur = db.conn.cursor()
+    db.create_from(test_swhids_sample, LIMIT, cur)
+
+    app = create_app(db)
+
+    with app.test_client() as test_client:
+        res = test_client.post("/api/1/known/", json=swhids)
+        assert res.status_code != 200