CertMonitor

Zero-dependency certificate monitoring and validation for Python. Native, portable, extensible, and secure.
All orchestration and logic are pure Python standard library. Advanced public key parsing and elliptic curve support are powered by Rust. No third-party Python dependencies.

⚡️ Why CertMonitor?

CertMonitor was born out of real-world frustration: outages and security incidents caused by expired certificates, missing Subject Alternative Names, or incomplete certificate chains. This tool is a labor of love—built to solve those pain points with a zero-dependency, native Python approach. All orchestration and logic are pure Python stdlib, but advanced public key parsing and elliptic curve support are powered by Rust for speed, safety, and correctness. CertMonitor is always improving, and your feedback is welcome!

from certmonitor import CertMonitor

with CertMonitor("example.com") as monitor:
    print(monitor.get_cert_info())
    print(monitor.validate())

This is a sample of the structured certificate info returned by monitor.get_cert_info():

{
  "subject": {
    "commonName": "example.com"
  },
  "issuer": {
    "organizationName": "DigiCert Inc",
    "commonName": "DigiCert TLS RSA SHA256 2020 CA1"
  },
  "notBefore": "2024-06-01T00:00:00",
  "notAfter": "2025-09-01T23:59:59",
  "serialNumber": "0A1B2C3D4E5F6789",
  "subjectAltName": {
    "DNS": ["example.com", "www.example.com"],
    "IP Address": []
  },
  "publicKeyInfo": {
    "algorithm": "rsaEncryption",
    "size": 2048,
    "curve": null
  }
}

This is a sample of the PEM format returned by monitor.get_raw_pem():

-----BEGIN CERTIFICATE-----
MIID...snip...IDAQAB
-----END CERTIFICATE-----

This is a sample of the DER format returned by monitor.get_raw_der() (as bytes, shown here as base64):

MIID...snip...IDAQAB

{
  "expiration": {
    "is_valid": true,
    "days_to_expiry": 120,
    "expires_on": "2025-09-01T23:59:59",
    "warnings": []
  },
  "subject_alt_names": {
    "is_valid": true,
    "sans": {"DNS": ["example.com", "www.example.com"], "IP Address": []},
    "count": 2,
    "contains_host": {"name": "example.com", "is_valid": true, "reason": "Matched DNS SAN"},
    "contains_alternate": {"www.example.com": {"name": "www.example.com", "is_valid": true, "reason": "Matched DNS SAN"}},
    "warnings": []
  }
}

• 🔒 Zero Dependencies: 100% standard library. No third-party Python packages required—ever.
• 🛡️ Certificate Validators: Modular checks for expiration, hostname, SANs, key strength, protocol, ciphers, and more.
• ⚡ High Performance: Async- and batch-friendly. Designed for speed and concurrency.
• 🧩 Extensible: Add your own custom validators for organization-specific checks.
• 🐍 Native Python First: Works out-of-the-box in any Python 3.8+ environment.
• 🦀 Rust-Powered Parsing: Certificate parsing and public key extraction are handled by a Rust extension for speed, safety, and correctness. This is required for advanced public key and elliptic curve features, but all orchestration and logic are pure Python stdlib.
• 📦 Portable: No system dependencies. Drop it into any project or CI pipeline.
• 📝 Comprehensive Docs: ReadTheDocs with usage, API, and advanced guides.

CertMonitor uses a powerful system of validators—modular checks that automatically assess certificate health, security, and compliance. Validators can:

• Detect expired or soon-to-expire certificates
• Ensure hostnames and SANs match
• Enforce strong key types and lengths
• Require modern TLS versions and strong cipher suites
• Allow you to add custom organization-specific checks

You can enable, disable, or extend validators to fit your needs, making CertMonitor ideal for continuous monitoring, compliance automation, and proactive security.

• expiration: Validates that the certificate is not expired.
• hostname: Validates that the hostname matches the certificate's subject alternative names (SANs).
• subject_alt_names: Validates the presence and content of the SANs in the certificate.
• root_certificate: Validates if the certificate is issued by a trusted root CA.
• key_info: Validates the public key type and strength.
• tls_version: Validates the negotiated TLS version.
• weak_cipher: Validates that the negotiated cipher suite is in the allowed list.

If published to PyPI:

pip install certmonitor

If not published, clone this repository and install locally:

git clone <repo-url>
cd certmonitor
pip install .

from certmonitor import CertMonitor

with CertMonitor("example.com") as monitor:
    cert_data = monitor.get_cert_info()
    validation_results = monitor.validate(validator_args={"subject_alt_names": ["www.example.com"]})
    print(cert_data)
    print(validation_results)

monitor = CertMonitor("example.com")
cert_data = monitor.get_cert_info()
validation_results = monitor.validate()
monitor.close()

You can also use an IPv4 or IPv6 address to retrieve and validate the SSL certificate. Note: Using an IP address may not match the certificate's hostname.

with CertMonitor("20.76.201.171") as monitor:
    cert = monitor.get_cert_info()
    validation_results = monitor.validate()
    print(cert)
    print(validation_results)

These methods are only available for SSL/TLS connections:

raw_der = monitor.get_raw_der()  # Returns DER bytes
raw_pem = monitor.get_raw_pem()  # Returns PEM string

You can retrieve and validate cipher suite information:

cipher_info = monitor.get_cipher_info()
print(cipher_info)

You can configure CertMonitor by specifying which validators to enable in the enabled_validators parameter. If not specified, it will use the default validators defined in the configuration.

By default, the following validators are enabled:

• expiration
• hostname
• root_certificate

CertMonitor can also read the list of enabled validators from an environment variable ENABLED_VALIDATORS. This is useful for configuring the validators without modifying the code.

Example:

export ENABLED_VALIDATORS="expiration,hostname,subject_alt_names,root_certificate,key_info,tls_version,weak_cipher"

CertMonitor automatically detects the protocol (SSL/TLS or SSH) for the target host. Most features are focused on SSL/TLS. SSH support is limited.

If an error occurs (e.g., connection failure, invalid certificate), CertMonitor methods will return a dictionary with an error key and details. Always check for errors in returned data:

cert = monitor.get_cert_info()
if isinstance(cert, dict) and "error" in cert:
    print("Error:", cert["message"])

This project is licensed under the MIT License. See the LICENSE file for details.