alibabacloud-tls-cert-diagnosis

Diagnose TLS/SSL certificate problems for a user-provided domain - trust chain verification, hostname/SAN matching, expiration check - with automatic DNS resolution and TCP connectivity root-cause analysis when a check fails. Use when the user reports a browser certificate error, HTTPS access fails and needs certificate-layer diagnosis, wants to verify a domain's TLS configuration, or asks for a certificate expiration check. Read-only diagnostics. Only checks domains the user explicitly provides. No write operations, no credentials required. Triggers: "certificate expired", "certificate not trusted", "SSL handshake failed", "hostname mismatch", "certificate check", "TLS certificate diagnosis", "HTTPS certificate error", "certificate validity check", "SAN mismatch", "certificate chain verification".

TLS Certificate Diagnosis

Diagnose TLS/SSL certificate problems for a user-provided domain: certificate not trusted, hostname/SAN mismatch, expiration issues, and HTTPS access failures. The check flow resolves DNS, tests TCP connectivity, then verifies the certificate trust chain, hostname match, and validity period. When a check fails, a network pre-check and DNS diagnosis run automatically to pinpoint the root cause.

Module Index

Module	Purpose	File
DNS Diagnosis	DNS status codes and diagnostic commands	references/dns_diagnosis.md
Prerequisites	System dependencies, OS compatibility, CA certificate setup	references/prerequisites.md
Output Schema	Formal JSON Schema for script output	references/output_schema.md

Load references on demand. Do not read all reference files unless the task requires them.

User Confirmation

• Before running any check, confirm the target domain with the user.
• If the user has not provided a domain, ask for it first. Never guess, derive, or scan for domains on your own.
• If you obtain the domain from task context rather than directly from the user, state the domain and its source explicitly before running any check.

Execution Principle

MANDATORY:

• Read-only: this skill only inspects and reports. It performs no write operations and requires no credentials of any kind.
• Single entry point: all checks MUST be executed through the entry script scripts/check_tls.py. Do not hand-assemble diagnostic command chains.
• User-provided targets only: only check domains the user explicitly provides.
• No scanning: never scan, sweep, or probe unknown or unspecified addresses.

Commands

Set the skill directory once, then run the entry script:

bash

SKILL_DIR=~/.qoderwork/skills/alibabacloud-tls-cert-diagnosis

Single Domain

bash

cd $SKILL_DIR && python3 scripts/check_tls.py example.com --pretty

Custom Port

bash

cd $SKILL_DIR && python3 scripts/check_tls.py example.com --port 8443 --pretty

Batch Check

Create a file with one domain per line (lines starting with # are ignored), then run:

bash

cd $SKILL_DIR && python3 scripts/check_tls.py --file domains.txt --pretty

Capabilities

#	Capability	Description
C1	Single-Domain Full-Chain Check	DNS resolution -> TCP connectivity -> trust chain verification, hostname/SAN matching, expiration check
C2	Abnormal Certificate Diagnosis	Detect and report certificate expired, certificate not trusted, and hostname mismatch, with the specific reason for each issue
C3	DNS Failure Root-Cause Diagnosis	When a check fails, classify the DNS failure (NXDOMAIN / SERVFAIL / REFUSED / TIMEOUT / CNAME-only) per references/dns_diagnosis.md
C4	Custom Port Check	Check a TLS endpoint on a non-default port via --port
C5	Batch Check	Check multiple domains from a file via --file, one domain per line
C6	Structured JSON Output	Machine-readable JSON result per references/output_schema.md

Platform-specific tool selection (macOS / Linux / Windows) and CA bundle paths are handled automatically by the entry script; see references/prerequisites.md for details.

Check Flow

text

Domain input
    |
    v
Run certificate check (openssl s_client)
    |
    +-- OK  -> output cert details (trust / hostname match / expiry)
    |
    +-- FAIL -> run network pre-check (nc on macOS, telnet on Linux, Test-NetConnection on Windows)
              |
              +-- if DNS fails -> run dig / nslookup DNS diagnosis
                    |
                    +-- NXDOMAIN: domain does not exist
                    +-- SERVFAIL: DNS server failure
                    +-- REFUSED:  DNS query refused
                    +-- TIMEOUT:  DNS server no response
                    +-- NOERROR no A record: only CNAME, follow CNAME chain

Output Format

Human-Readable Summary

Normal Certificate

text

Domain       : example.com
Port         : 443
Status       : OK
  Trust      : trusted
  Hostname   : match
  Validity   : 2025-01-15 ~ 2026-01-15
  Days left  : 245
  Issuer     : DigiCert TLS RSA SHA256 2020 CA1
  Subject    : CN=www.example.org
  SAN        : www.example.org, example.org, example.com, www.example.com

Abnormal Certificate

text

Domain       : expired.example.com
Port         : 443
Status       : abnormal (3 issues)
  Trust      : trusted
  Hostname   : mismatch
  Validity   : 2023-01-15 ~ 2024-01-15
  Days left  : expired 134 days
  Issuer     : Let's Encrypt R3
  Issues     :
    - certificate expired
    - verification failed: certificate has expired
    - hostname mismatch: SAN does not contain target domain

Network Unreachable (with DNS diagnosis)

text

Domain       : nonexistent.example.com
Port         : 443
Status       : abnormal (1 issue)
  Network    : unreachable
  Issue      : network unreachable - TCP connection failed;
               dig: domain does not exist (NXDOMAIN)

JSON Output

The entry script outputs JSON. See references/output_schema.md for the formal schema.

Check Items

Check Item	Description	On Failure
DNS Resolve	Query A / AAAA records	Report NXDOMAIN / SERVFAIL / REFUSED / TIMEOUT
TCP Reachable	Test port connectivity on resolved IPs	Report connection failure reason
TLS Handshake	Fetch server certificate	Report "no certificate received"
Trust Chain	Verify certificate chain against system CA bundle	Verify code 0 = trusted; otherwise report error
Hostname Match	Match domain against certificate SAN (wildcard restricted to one level)	Report mismatch
Expiry	Parse notBefore / notAfter	Report expired or not yet valid

Examples

Example 1: User: "My browser says the certificate for shop.myshop.com is not trusted, please check it."

bash

cd $SKILL_DIR && python3 scripts/check_tls.py shop.myshop.com --pretty

Example 2: User: "Our API runs TLS on port 8443, can you verify the certificate expires soon?"

bash

cd $SKILL_DIR && python3 scripts/check_tls.py api.example.com --port 8443 --pretty

Example 3: User: "Check the certificates for all domains in this list file."

bash

cd $SKILL_DIR && python3 scripts/check_tls.py --file domains.txt --pretty

Notes

• Supports macOS, Linux, and Windows 10/11. On Windows, the script uses nslookup for DNS, PowerShell Test-NetConnection for TCP, and openssl (requires standalone OpenSSL for Windows). Windows CA auto-detection checks the OpenSSL-Win64 install path.
• Rely on system binaries. macOS/Linux use openssl, dig, nc, and telnet. Windows uses openssl, nslookup, and PowerShell Test-NetConnection. No external Python libraries are required.
• Only checks domains explicitly provided by the user; never probes unknown or unspecified addresses. This prevents accidental scanning of internal networks without explicit user intent.
• Set a default timeout of 5 seconds per domain. This balances between waiting for slow responses and failing fast on unreachable targets. Increase with --timeout-ms for high-latency networks.
• Match wildcard certificates *.example.com against only one-level subdomains (e.g. a.example.com). Reject multi-level matches (e.g. a.b.example.com). This follows RFC 6125 Section 6.4.3, which restricts wildcard certificates to a single label to prevent overly broad matching that could violate the subscriber's intended scope.
• If DNS returns only a CNAME with no A record, follow the CNAME chain recursively until finding the final A record IP. Some domains (e.g. CDN fronted domains) resolve through multiple CNAME hops. Stopping at the first CNAME would produce no IP and a false negative, so recursive resolution is required for accurate diagnosis.