certinspect 0.7.0

Command-line TLS certificate inspector

certinspect

Command-line TLS certificate inspector.

Given one or more domains (or a .pem/.der file), it reports:

• Validity and days to expiry
• Total validity period
• Subject and issuer
• Subject Alternative Names (SAN)
• Signature algorithm and key size
• SHA-256 fingerprint
• CA flag and self-signed flag
• Key usage and extended key usage
• Weak-crypto warnings
• Negotiated TLS version and cipher
• Hostname match against the certificate

It can also:

• Verify the chain + OCSP revocation against the system trust store (--verify)
• Show the chain presented by the server (--chain)
• Pin the certificate by SHA-256 fingerprint (--pin)
• Inspect many hosts at once with text or JSON output (batch mode, --json)
• Inspect hosts in parallel in batch mode (--concurrency)
• Inspect certificates behind STARTTLS — SMTP, IMAP, POP3, FTP (--starttls)
• Emit monitoring output for Nagios/Icinga and Prometheus (--exporter)

Requirements

• Python >= 3.10

Installation

pip install certinspect

From source (development)

python3 -m venv .venv
source .venv/bin/activate
pip install -e ".[dev]"

Usage

# Inspect a host
certinspect example.com

# A full URL or host:port works too (scheme and path are ignored)
certinspect https://example.com/login
certinspect example.com:8443

# Multiple hosts at once (batch mode)
certinspect example.com github.com api.example.com

# Inspect many hosts in parallel (output order is preserved)
certinspect example.com github.com api.example.com --concurrency 10

# Custom port
certinspect example.com --port 8443

# Custom connection timeout in seconds (default: 5)
certinspect example.com --timeout 10

# JSON output (always a list of objects)
certinspect example.com --json

# Inspect a local certificate
certinspect --file ./certificate.pem

# Custom expiry warning threshold (default: 30 days)
certinspect example.com --days 14

# Only print certificates that have a problem
certinspect example.com github.com --quiet

# Verify the certificate chain against the system trust store
certinspect example.com --verify

# Show the certificate chain presented by the server
certinspect example.com --chain

# Fail (exit 7) unless the fingerprint matches the expected pin
certinspect example.com --pin AA:BB:CC:...

# Read targets from a file (or '-' for stdin)
certinspect --input hosts.txt
cat hosts.txt | certinspect --input -

# Save the fetched certificate as PEM
certinspect example.com --export ./fetched.pem

# Inspect a certificate behind STARTTLS (smtp, imap, pop3, ftp)
# The protocol's standard port is used unless --port is given
certinspect mail.example.com --starttls smtp
certinspect mail.example.com --starttls imap --port 143

# Monitoring output: a Nagios/Icinga plugin line per target
# (exit code follows the plugin convention: 0=OK, 1=WARNING, 2=CRITICAL)
certinspect example.com --exporter nagios

# Monitoring output: Prometheus textfile-collector metrics
certinspect example.com github.com --exporter prometheus

# Print the version
certinspect --version

Example

$ certinspect pypi.org --verify
=== pypi.org ===
Subject:        CN=pypi.org
Status:         VALID

Issuer:         CN=GlobalSign Atlas R3 DV TLS CA 2025 Q4,O=GlobalSign nv-sa,C=BE
Valid from:     2025-12-28 04:33:08+00:00
Valid until:    2027-01-29 04:33:07+00:00
Days to expiry: 217
Total validity: 396 days

Serial number:  1587345912129534630556007389588586994
Signature:      sha256WithRSAEncryption
Key size:       2048 bit
Fingerprint:    15:58:1C:41:02:3F:07:89:85:31:4E:7D:4C:4F:8A:CA:BF:05:C7:F6:...
CA:             False
Self-Signed:    False
TLS version:    TLSv1.3
Cipher:         TLS_AES_128_GCM_SHA256
Key usage:      digital_signature, key_encipherment
Ext. key usage: serverAuth, clientAuth
Hostname match: True
Chain trusted:  True
Revocation:     GOOD

SAN:
  - pypi.org
  - *.pypi.org
  - www.pypi.org
  - donate.pypi.org

With --verify, certinspect opens a fully verified TLS handshake (chain + hostname against the Python/OpenSSL trust store) and, when the certificate advertises an OCSP responder, queries it for the revocation status. OCSP is soft-fail: an unreachable responder reports UNAVAILABLE and does not change the exit code, while a REVOKED status fails with exit code 6. Revocation is not checked via CRLs.

Options

Option	Description
target...	One or more domains, URLs or host:port to inspect. Omit when using --file.
--file PATH	Inspect a local certificate (PEM or DER) instead of a host.
--port N	TCP port to connect to (default: 443).
--timeout N	Connection timeout in seconds (default: 5).
--json	Print the result as JSON instead of human-readable text.
--quiet	Only print certificates that have a problem.
--verify	Verify the chain + OCSP revocation, system trust store (hosts only).
--chain	Show the certificate chain presented by the server.
--pin SHA256	Fail (exit 7) unless the SHA-256 fingerprint matches (colons/case ignored).
--input PATH	Read extra targets from a file, one per line ('-' for stdin).
--days N	Warn if the certificate expires within N days (default: 30).
--export PATH	Save the inspected certificate as a PEM file at PATH.
--starttls {smtp,imap,pop3,ftp}	Upgrade a plaintext connection to TLS before inspecting (standard port unless --port is given).
--exporter {nagios,prometheus}	Emit machine-readable monitoring output (ignores --quiet).
--concurrency N	Inspect up to N hosts in parallel in batch mode (default: 1; order is preserved).
--version	Print the version and exit.

Monitoring

Use --exporter to plug certinspect straight into a monitoring stack. Both formats report every target, including hosts that could not be reached.

nagios emits one Nagios/Icinga plugin line per target with perfdata and exits with the plugin convention (0 OK, 1 WARNING, 2 CRITICAL); an unreachable host is CRITICAL:

$ certinspect example.com expired.example.com --exporter nagios
OK: example.com certificate VALID (217 days to expiry) | days=217;30;0
CRITICAL: expired.example.com certificate EXPIRED (-3 days to expiry) | days=-3;30;0

prometheus emits textfile-collector metrics (certinspect_up, certinspect_cert_expiry_days, certinspect_cert_valid), keeping the normal worst-status exit code:

$ certinspect example.com --exporter prometheus
# HELP certinspect_up Whether the target could be inspected (1) or not (0).
# TYPE certinspect_up gauge
certinspect_up{target="example.com"} 1
# HELP certinspect_cert_expiry_days Days until the certificate expires.
# TYPE certinspect_cert_expiry_days gauge
certinspect_cert_expiry_days{target="example.com"} 217
# HELP certinspect_cert_valid Whether the certificate is within its validity window (1) or not (0).
# TYPE certinspect_cert_valid gauge
certinspect_cert_valid{target="example.com"} 1

Exit codes

Designed for automation (cron, CI, monitoring scripts). In batch mode the worst code across all targets is returned.

Code	Meaning
0	Valid certificate
1	Runtime error (network, file, parse)
2	Command-line usage error
3	Expiring within the --days threshold
4	Expired or with invalid dates
5	Hostname does not match the certificate
6	Chain not trusted or revoked (--verify)
7	Fingerprint does not match --pin

Example in a script:

certinspect yoursite.com --days 21
case $? in
  0) ;;                                        # all good
  3) echo "Expiring" | mail -s "Warning" [e-mail] ;;
  4) echo "Expired"  | mail -s "Urgent"  [e-mail] ;;
  5) echo "Bad host" | mail -s "Urgent"  [e-mail] ;;
  *) echo "Check failed" ;;
esac

Development

# Tests
pytest

# Lint and formatting (Ruff)
ruff check src tests
ruff format src tests

License

MIT — see LICENSE.