Can I test private (RFC1918) NTP servers online?

Yes. Use Bridge Mode to test NTP servers on private networks (192.168.x.x, 10.x.x.x, 172.16-31.x.x). Install the lightweight Node.js bridge on your local machine, and it will relay NTP queries to internal servers.

How does NTP server validation work?

The validator sends an NTPv4 packet to the target server and analyzes the response: stratum level, clock offset, round-trip delay, reference ID, and leap indicator. Results are compared against our Stratum 1 GNSS reference.

What does the NTP stratum level mean?

Stratum indicates distance from the reference clock. Stratum 0 is the atomic clock/GPS itself, Stratum 1 is directly connected to it, Stratum 2 syncs from Stratum 1, and so on. Stratum 16 means unsynchronized. For reliable time, use Stratum 1-3 servers.

Online NTP Validator | Test NTP Servers & RFC1918

Test Mode Selection

Basic Mode

Test your browser time against our NTP reference. No setup required.

Bridge Mode

Test any NTP server via local bridge. Supports RFC1918 IPs.

CLI Script

Download shell script for server-side testing.

Basic Time Test

Test your system's time synchronization against our NTP server, synced to our Stratum 1 GNSS reference.

NTP Bridge Testing

Bridge Not Connected

Start the local bridge server to test NTP servers directly.

Quick Start:

# 1. Download and install
cd /tmp && curl -sL https://online-ntp-validator.com/bridge/ntp-bridge.tar.gz | tar xz
cd ntp-bridge && npm install

# 2. Start the bridge
node server.js
# Bridge running on ws://localhost:8080

# 1. Prerequisites: Node.js (via Homebrew if needed)
brew install node

# 2. Download and install
cd /tmp && curl -sL https://online-ntp-validator.com/bridge/ntp-bridge.tar.gz | tar xz
cd ntp-bridge && npm install

# 3. Start the bridge
node server.js
# Bridge running on ws://localhost:8080

# PowerShell - 1. Prerequisites: Node.js
# Download from https://nodejs.org/

# 2. Download the bridge
Invoke-WebRequest -Uri "https://online-ntp-validator.com/bridge/ntp-bridge.zip" -OutFile "$env:TEMP\ntp-bridge.zip"
Expand-Archive -Path "$env:TEMP\ntp-bridge.zip" -DestinationPath "$env:TEMP\ntp-bridge" -Force
cd "$env:TEMP\ntp-bridge"

# 3. Install and start
npm install
node server.js
# Bridge running on ws://localhost:8080

Download the bridge files using the curl commands above.

Bridge URL:

CLI Testing Script

Download our bash script for server-side NTP testing.

# One-liner test
curl -sL https://ntp.rdem-systems.com/ntp-check.sh | bash

# Or download and run
wget https://ntp.rdem-systems.com/ntp-check.sh
chmod +x ntp-check.sh
./ntp-check.sh

Download ntp-check.sh

NTP Compliance Validation Checklist

Download our 15-point checklist to ensure your NTP infrastructure meets audit requirements:

Infrastructure

Multiple NTP sources configured (≥4)
Stratum 1 or 2 servers used
Geographic diversity of sources
Internal NTP hierarchy defined
Failover mechanisms in place

Security

UDP 123 firewall rules documented
NTP amplification protection
Access control lists configured
Monitoring and alerting active
Logs retained per policy

Validation

Offset within acceptable range
No false tickers detected
Reach value at 377
Regular sync verification
Documentation up to date

Related tools — Quick NTP diagnostic at check-ntp.net · NTS compatibility test at ntp-tester.eu

About this validator — An independent NTP server accuracy verification tool provided by RDEM Systems. Validation is performed against GNSS/PPS Stratum 1 references on our dedicated infrastructure. We actively contribute to the NTP Pool project →
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Online NTP Validator — Test NTP Servers & RFC1918