Free NZB Checker: Test Availability Across 7 Usenet Backbones
Upload an .nzb file and see, in about a minute, how many of its articles each Usenet backbone can still deliver – so you know before downloading whether your provider is likely to complete it.
Checking your NZB …
A check usually takes 20–90 seconds. Keep this tab open – the result appears here automatically.
Complete on 1 backbone, likely repairable on 2 more
6.1 GB · 64 files + 9 PAR2 files (10 % recovery data)
| Backbone | Tested articles available | Missing (estimated) | Status | Tested via |
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Download as usual.
Download all PAR2 files – SABnzbd and NZBGet try the repair automatically.
Add a backup provider on a backbone marked Complete or Repairable, e.g. a block account. How block accounts work
How the NZB check works
Upload your NZB
Drag and drop or choose an .nzb file. We read the list of article IDs inside it. The file itself never leaves your browser.
We test every backbone
For each of the 7 backbones we request the articles – all of them, or a random sample for large NZBs – through one representative provider, like a download client would. No content is saved.
You see the availability
Per backbone: the share of tested articles that were available, plus an estimate whether PAR2 recovery data can repair the gaps.
How to read your result
- ✓ Complete
- All tested articles were available.
- ↻ Repairable
- Some tested articles were missing, but the recovery data in the NZB may be enough to repair them.
- ✕ Incomplete
- The missing articles exceed the estimated repair capacity.
Availability is measured at the moment of the check; “Repairable” and “Incomplete” are estimates. When a sample is tested, untested articles can still be missing – so no result guarantees a successful download. Read our full test method.
Usenet backbone comparison: who delivers the most articles?
Loading the latest figures…
| # | Backbone | Availability | Tested via |
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What is an NZB checker?
An NZB checker – also called an NZB availability or completion checker – tests whether the Usenet articles listed in an NZB file can still be downloaded, before you start the download.
NZB Mentor is a free, independent NZB checker. It requests the articles of your NZB from 7 Usenet backbones – Abavia, Giganews, Its Hosted, Netnews, Omicron, UsenetExpress and Uzo Reto – and shows the share of tested articles each one delivered. The result is a measurement at one point in time, not a guarantee.
What is a Usenet backbone?
A Usenet backbone is the server infrastructure that stores Usenet articles and exchanges them with other backbones. Only a handful of backbones exist, but there are dozens of Usenet providers: many providers rent access to an existing backbone and sell it under their own brand. Providers on the same backbone therefore usually have the same articles, even if price and features differ.
Checking several backbones is useful because each one handles takedowns and retention differently – an NZB can be complete on one and incomplete on another. The check shows which backbone can still deliver your download, and which one makes a good backup. For long-term numbers, see the current Usenet backbone performance ranking.
Why do NZB downloads fail?
A binary post on Usenet is split into hundreds or thousands of articles. If only some of them are missing on your provider's backbone, the download is incomplete. Missing Usenet articles usually have one of three causes:
- Takedowns: rights holders send removal notices (DMCA in the US, NTD in Europe), and each backbone processes them on its own.
- Retention: the post is older than the backbone keeps articles.
- Propagation: some articles never reached every backbone.
How to Improve NZB Completion Rates
Incomplete NZB downloads almost always mean that some articles are missing on your provider's backbone. Three things help:
- Keep the PAR2 files. Most posts include PAR2 recovery data. If only a small share of articles is missing, your download client can usually rebuild the missing parts.
- Add a backup provider on a different backbone. Providers on the same backbone tend to miss the same articles. A second account – often a prepaid block account – on another backbone can fill the gaps.
- Don't rely on retention alone. Retention says how long articles are kept, not whether a specific article still exists. Measured availability is the better guide.
Wondering which Usenet backbone offers the best article availability? Explore our real-world Usenet retention comparison.
Questions about NZB checks
What exactly does NZB Mentor check?
NZB Mentor reads the article IDs in your NZB file and requests those articles from 7 Usenet backbones. NZBs with up to 100 articles are tested completely; for larger NZBs it tests a random sample, spread evenly across the NZB. The result shows, per backbone, the share of tested articles that were available and an estimate whether PAR2 recovery data can repair the gaps.
Does a “Complete” result guarantee that my download will work?
No. “Complete” means that all tested articles were available at the moment of the check. With a sample check, untested articles can still be missing, and articles can be removed after the check.
Does NZB Mentor store my NZB file or the downloaded content?
No. Your browser reads the NZB file and sends only the article IDs; the file itself never leaves your browser. No content is saved or reassembled. Anonymous counts (post age and availability per backbone) are added to our statistics. What we store
Is NZB Mentor free and independent?
Yes. NZB Mentor is free, needs no account and is not paid by or affiliated with any Usenet provider or backbone. Rankings come only from measured data. About our independence