Full HTTP probe
Run /check/t.co to see live HTTP status, response time, and 24h history alongside this cert.
TLS / SSL certificate
t.co TLS certificate
t.co
port 443
172.66.0.227
VALID
1s ago
What this means
Browsers will accept this certificate. Plan a renewal before the expiry date below — most CAs auto-renew at 30 days remaining.
Certificate details
- Subject CN
- t.co
- Issuer
- Let's Encrypt / E8
- Valid from
- Mar 13, 2026, 10:18 AM (42d ago)
- Valid to
- Jun 11, 2026, 10:18 AM (1s ago)
- Days remaining
- 47
- Key
- EC prime256v1
- Signature
- ECDSA-PRIME256V1
- Hostname match
- yes
- SHA-256 fingerprint
- 3A:70:14:1C:DE:81:FB:F9:CF:CD:F8:6A:BC:28:AD:94:3D:76:50:FB:7C:31:DD:54:21:9A:F0:8F:F1:8D:D1:7C
Subject Alternative Names (1)
t.co
What to try next
Renewal reminder
Set a 30-day-before-expiry calendar reminder. Most outages caused by expired certs come from missed renewals.
Check related
Compare with related services or apex/subdomain combinations to spot inconsistencies.
Methodology
- Probe
- We open a TLS handshake to port 443 with the supplied hostname as the SNI, read the peer certificate via getPeerCertificate(true), and validate the hostname against subjectAlternativeName via tls.checkServerIdentity.
- Counts as DOWN
- The TLS handshake fails entirely (TCP refused, handshake timeout, or rejected ClientHello) — we couldn't read a certificate at all.
- Counts as DEGRADED
- Reserved for soon-to-expire certificates and warning-only validation issues like a self-signed cert. Browsers may still warn even when our check labels the cert valid.
- Detail
- All certificate details come from getPeerCertificate(true) on the established socket. We do not enumerate cipher suites, test downgrade attacks, or scan for protocol-level weaknesses; this is read-only certificate inspection.
- Cadence
- Every 5 minutes, in parallel across 4 monitoring regions (US East Virginia, US West Oregon, Europe London, Asia Singapore).
- Rate-limited targets
- If a host returns 429 or consistently drops connections from our IPs, we cap retries at 3 and report the last observed status — we do not flood the target to confirm the outage.
- Data source
- Direct probes from our monitoring infrastructure. We do not aggregate crowd reports, Twitter mentions, or DownDetector signals — every result on this page is a live network request.