Evaluating NTP servers with NTPinfo
The ‘internet.nl’ for NTP-based time services
We have launched a new website: ntpinfo.sidnlabs.nl. NTPinfo allows users to evaluate the properties of NTP servers, such as their accuracy, time source and geo location. The site was developed by students at Delft University of Technology (TU Delft) as part of the bachelor’s course ‘Software Project’ with us acting as their clients.
Why NTP matters
Accurate, synchronised clocks are crucial for the modern world. They keep everything running smoothly – from financial transactions and power grids to telecom networks. On the internet, many core systems rely on synchronised time to work correctly. Services like secure web connections (TLS), DNS security (DNSSEC) and digital certificates all depend on accurate timing to verify what’s valid and what’s not.
When clocks go wrong, the results can be messy. In one major incident in 2012, the U.S. Naval Observatory accidentally distributed time information that was off by 10 years. The mistake caused widespread disruptions, knocking network routers and Active Directory servers offline. Even though it was not an attack, it behaved like one.
NTPinfo: the ‘internet.nl’ for NTP-based time services
Currently there’s no website that allow users to check how accurate an NTP server really is. The main issue is that it requires measurements that cannot be run in a browser. You would therefore have to run commands on a command-line interface to get results, which is cumbersome.
To solve that problem, we proposed NTPinfo, a website that enables users to easily evaluate NTP servers. Our inspiration was internet.nl, a popular website that enables users to easily check the (security) properties of domain names and their internet connections, amongst other things.
The core idea was to provide a website where users can evaluate NTP servers of their choice, against 2 time sources. First, our GPS/DC77-synced public time servers provided by TimeNL. In addition, it would use vantage points in the vicinity of the user, provided by RIPE Atlas probes. That set-up means a user can compare results from our servers in the Netherlands against probes in their own area.
Software project course at TU Delft
Instead of developing the tool ourselves, we submitted a project proposal for NTPinfo to the Software Project (CSE2000) course in the Computer Science and EngineeringTU Delft’s bachelor programme. On this course, groups of 5 students work on a project that is commissioned by the faculty or an external ‘client’.
Our role in the project was to act as the client– defining what features we wanted for NTPinfo. TU Delft provided support and supervision: a teaching assistant and a coach guided the student team, helping them make technical decisions along the way, such as which framework to use.
We had a round of interviews with various student groups and picked one, whose members were Călin-Mihai Olaru, Horia-Andrei Botezatu, Șerban Orza, Mihai-Valentin Nicolae, George-Matei Andrei. During the project, we had weekly meetings with the students and in the end they delivered the final software, and we deployed the website at ntpinfo.sidnlabs.nl.
The result: ntpinfo.sidnlabs.nl
NTPinfo evaluates the accuracy of NTP servers by comparing them against 2 sources: our own satellite-synced time servers at time.nl and a nearby RIPE Atlas probe, which is not satellite synced but uses different methods to sync clocks.
Figure 1 shows a screenshot of the website. As an example, it shows the properties of the NTP service time.apple.com, which at the time had an offset of 0.5ms from the time.nl servers and 0.153ms offset with RIPE Atlas. As such, we can see that this server is accurate by comparison with both time.nl and ripe atlas vantage points.
(Click on the image to enlarge it.)
This dual comparison gave also gave the students a clearer picture of how well a time server performs — both from the browser perspective and from a RIPE Atlas probe at a nearby location. It’s a simple way for the students to check if an NTP server is accurate enough for the user’s needs.
Public feedback and real-world impact
NTPinfo got attention from the wider internet community, with feedback coming in from the IETF NTP working group, the NTP Pool Forum and RIPE Atlas list. Even better: one of the students was invited and sponsored to present the tool at ICANN 84 (October 2025) in Dublin, during the Tech Day session, and at the forthcoming RIPE91 meeting. They’re also working on further improvement of the tool.
For students, this kind of exposure is huge – it puts them in front of real-world operators early in their careers and opens doors for future opportunities.
Collaboration that pays off
This project is a great example of how academic collaboration can really deliver. It was a win for the students, who got to work on a real-world challenge, build something meaningful, and receive public feedback. It was a win for us as clients in the project, because we now run NTPinfo as a service and help the community with an open-source tool. Also, we helped to train the next generation in NTP and internet engineers, which is a long-term win for the internet.
If you’re in the industry, we highly encourage you to submit a proposal to TU Delft. They’re always looking for real-world challenges for students to tackle. Any company can apply via the Software Project course site – the next deadline is Sunday, March 15th, 2026.
What’s next
We’re planning a guest post from the students in which they’ll dive into the technical details of NTPinfo. You can also watch their presentation of NTPinfo online at both RIPE91 (21 Oct 2025) and ICANN84 Tech Day (27 Oct 2025).
