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Check error messages explained
What FastPing check and validation errors mean, from connection refused and timeouts to certificate and DNS errors, and how to fix each one.
| Message | What it means | What to do |
|---|---|---|
Private or reserved addresses are not allowed. | The IP address is private, loopback, link-local or reserved (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8, 100.64.0.0/10…). FastPing never connects to such addresses. | Use the public address of the service. |
Private hostnames are not allowed. | Names such as localhost or ones ending in .local, .internal or .localhost only exist inside a private network. | Use the public hostname. |
Invalid hostname. | The text is not a valid domain name (spaces, underscores, missing dot…). | Enter only the host, such as example.com, without paths or ports. |
Only http and https URLs are supported. | The URL uses another scheme, such as ftp:// or ws://. | Use http:// or https://. |
Credentials in URLs are not allowed. | The URL contains user:password@. | Remove the credentials; for authenticated endpoints, use an API monitor with an Authorization header. |
Enter a port. | This monitor type needs a port. | Enter the port number. |
Port must be between 1 and 65535. | The port is outside the valid range. | Enter a port from 1 to 65535. |
Verify the domain first. | Security scans only run on verified domains. | Verify the domain under Verified domains. |
This monitor type requires the Security exposure scans add-on. Upgrade under Plan & billing. | The type needs an add-on your plan does not include. | Add it to your plan. |
| Message | What it means | What to do |
|---|---|---|
Could not resolve shop.example.com. | DNS has no address for the name. | Check the A/AAAA records and spelling. |
Hostname resolves to a private or reserved address. | The DNS record points to a private address. | Point the record to the public address, or monitor another name. |
connect ECONNREFUSED 203.0.113.10:443 | The host refused the connection: nothing listens on the port, or a firewall rejects it. | Start the service or open the port for FastPing. |
socket hang up | The connection was closed before a response arrived. | Often a WAF, proxy or rate limiter; see the firewall guide. |
read ECONNRESET | The connection was reset mid-way. | Same causes as above; also overloaded servers. |
Timed out after 15s | No response within the monitor's timeout. | Check the server; raise the timeout for slow endpoints. |
Check timed out | The whole check took longer than 90 seconds and was stopped. | The target is extremely slow or stalls connections. |
Each monitor type's article lists its own messages:
- Website (HTTP) monitors: status codes, timeouts, certificate errors, redirects.
- Keyword monitors and API (JSON) monitors: keyword and JSON assertions.
- Ping monitors (ICMP) and TCP port monitors: packet loss, open, closed and filtered ports.
- DNS record monitors: missing records, resolver errors, expected values.
- SSL/TLS certificate monitors:
CERT_HAS_EXPIRED,UNABLE_TO_VERIFY_LEAF_SIGNATUREand other certificate codes. - Domain expiry monitors: RDAP availability and lookups.
- Game server monitors: query timeouts and protocol errors.
- Heartbeat monitors for cron jobs and scheduled tasks: overdue pings and URL responses.
- Mail server monitors (SMTP, IMAP, POP3)
- UDP port monitors
- WebSocket monitors
- HTTP/2 and HTTP/3 monitors