Fast and powerful SSL/TLS server scanning library.
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Fast and powerful SSL/TLS server scanning library for Python 2.7 and 3.4+.


SSLyze is a Python library and a CLI tool that can analyze the SSL configuration of a server by connecting to it. It is designed to be fast and comprehensive, and should help organizations and testers identify mis-configurations affecting their SSL/TLS servers.

Key features include:

  • Fully documented Python API, in order to run scans and process the results directly from Python.
  • New: Support for TLS 1.3 (draft 23) and the ROBOT vulnerability.
  • Scans are automatically dispatched among multiple processes, making them very fast.
  • Performance testing: session resumption and TLS tickets support.
  • Security testing: weak cipher suites, insecure renegotiation, CRIME, Heartbleed and more.
  • Server certificate validation and revocation checking through OCSP stapling.
  • Support for StartTLS handshakes on SMTP, XMPP, LDAP, POP, IMAP, RDP, PostGres and FTP.
  • Scan results can be written to an XML or JSON file for further processing.
  • And much more!

Getting started

SSLyze can be installed directly via pip:

pip install --upgrade setuptools
pip install --upgrade sslyze
python -m sslyze --regular "[2607:f8b0:400a:807::2004]:443"

SSLyze has been tested on the following platforms: Windows 7 (32 and 64 bits), Debian 7 (32 and 64 bits), macOS Sierra

Usage as a library

SSLyze can be used as a Python module in order to run scans and process the results directly in Python. Full documentation is available here.

A simple example follows:

# Setup the server to scan and ensure it is online/reachable
hostname = u''
    server_tester = ServerConnectivityTester(
    server_info = server_tester.perform()
except ServerConnectivityError as e:
    # Could not establish an SSL connection to the server
    raise RuntimeError('Error when connecting to {}: {}'.format(e.server_info.hostname, e.error_message))

# Run one scan command synchronously to list the server's TLS 1.0 cipher suites
print(u'\nRunning one scan command synchronously...')
synchronous_scanner = SynchronousScanner()
command = Tlsv10ScanCommand()
scan_result = synchronous_scanner.run_scan_command(server_info, command)
for cipher in scan_result.accepted_cipher_list:
    print(u'    {}'.format(

More advanced examples (such as running scan commands concurrently) are available in the file and in the SSLyze documentation.

Windows executable

A pre-compiled Windows executable is available in the Releases tab. The package can also be generated by running the following command:

python.exe build_exe

How does it work ?

SSLyze is all Python code but it uses an OpenSSL wrapper written in C called nassl, which was specifically developed for allowing SSLyze to access the low-level OpenSSL APIs needed to perform deep SSL testing.

Where do the trust stores come from?

The trust stores (Mozilla, Microsoft, etc.) used by SSLyze for certificate validation are downloaded from the Trust Stores Observatory.

The trust stores can be updated to the latest version, using either the CLI:

python -m sslyze --update_trust_stores

or the Python API:

from sslyze.plugins.utils.trust_store.trust_store_repository import TrustStoresRepository



Copyright (c) 2018 Alban Diquet

SSLyze is made available under the terms of the GNU Affero General Public License (AGPL). See LICENSE.txt for details and exceptions.