NTP Server Test Online Tool

Technical Details

Check reachability, offset, and delay of any Network Time Protocol (NTP) or SNTP server over IPv4 and IPv6. Compare your target server's time against our accurate stratum 2 reference. If a domain resolves to multiple A or AAAA records, the tool automatically tests all associated IP addresses.

The stratum metric defines a server's hierarchical distance from the primary reference clock. Stratum 1 servers are directly connected to highly accurate hardware time sources (Stratum 0, such as GPS, atomic, or radio clocks). A Stratum 2 server, like our reference, synchronizes with Stratum 1 sources. A lower stratum number indicates fewer network hops to the master clock. A stratum value of 16 means the server is unsynchronized. This is normal during the initial synchronization process, but a constant stratum 16 indicates a synchronization failure.

The offset metric indicates the calculated time difference between the target server's clock and our reference, revealing precisely how far ahead or behind its system time is. An offset closer to zero indicates higher accuracy. Naturally, a server with a lower stratum number should exhibit an offset closer to zero due to fewer network hops from the master clock. According to Internet Standards, an offset within tens of milliseconds (up to ±50 ms) is expected and considered accurate over the public internet.

The delay metric represents the total round-trip time (RTT) of the request, including both network latency and the server's internal processing time. This value heavily depends on physical distance. Our reference server is located in Germany. For example, the maximum expected delay is around 350 ms for servers located in New Zealand, as it is the geographic antipode of Germany and represents the longest possible routing path. While distant servers naturally exhibit higher delay, an RTT significantly higher than the ping to this website may indicate network congestion, server overload, or routing inefficiencies.

It uses ntpdate -q to perform a standard time synchronization query over UDP port 123. Because full NTP and Simple Network Time Protocol (SNTP) share the exact same packet structure, this tool works seamlessly for testing both full NTP servers (Linux, Windows, FreeBSD, Unix) and SNTP servers, such as embedded devices, routers, switches, firewalls, IP cameras, Digital Video Recorders (DVR), Internet of Things (IoT), dedicated hardware appliances, and all NTP/SNTP servers in general.

Common Connection Issues

The following steps may help you pass this test in case of trouble:

Verify that your server and NTP service are up and running.
Verify that the domain's DNS is resolving to the correct IP addresses, if you're entering a hostname.
Verify that your server's UDP 123 port is accessible from this website's IPv4 and IPv6 addresses: 173.249.29.54 and 2a02:c207:1:3253:1::1
Verify that the time sources of your server are synchronizing correctly.

Save Your Results

You can optionally save your results and share them with your team as evidence for troubleshooting tickets, scientific documentation, IT compliance audits, or any other purpose. This helps satisfy the strict evidence and network monitoring requirements of major cybersecurity frameworks such as ISO 27001, SOC 2, PCI DSS, and HIPAA. We commit to storing your results for a minimum period of 5 years and a maximum of 10 years, after which the saved results are permanently deleted from our servers.

Related Resources

Recommended for Linux server admins and Linux users:
How to join your Linux server to the NTP pool project
How to query and test an NTP server using ntpdate