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Validate a UBL invoice

Check your e-invoice against the applicable rules, with guidance on returned findings. Free within the daily limit.

In short

Check an invoice against its applicable EN 16931 and national rule set. Read each finding and guidance on what to correct. Free, 5 a day without an account.

Klarbon's UBL validator checks a UBL 2.1 invoice or credit note against the EN 16931 business rules for UBL. When the file declares Peppol BIS Billing 3.0, XRechnung or the Dutch NLCIUS, it runs that rule set instead. Returned findings include rule codes and guidance where available. Free for five checks a day, twenty with a free account.

What does the validator check?

A UBL invoice is an XML file in the OASIS Universal Business Language (OASIS UBL 2.1). Its cbc:CustomizationID says which rules it follows, and Klarbon picks the rule set from it:

The file declares Rule set applied
EN 16931 only EN 16931 1.3.17 for UBL (CEN/TC 434 artefacts)
Peppol BIS Billing 3.0 Peppol BIS Billing 3.0 rules (OpenPeppol), including EN 16931
XRechnung 3.0 XRechnung 3.0.2 rules for invoices, including EN 16931; UBL credit notes are not supported yet
NLCIUS SI-UBL 2.0 rules for invoices, including EN 16931; UBL credit notes are not supported yet
UBL.BE not checked; the UBL.BE rule set is not available in Klarbon

The report names the rule set and its version. Checking UBL is in beta. More in what is UBL.

How do I validate a UBL file?

  1. Upload the XML file. On a phone, pick it from Files, Mail or your downloads.
  2. Read the report. Returned findings show the rule code and severity, with a business term, source location and correction guidance where available.
  3. Correct and check again in your invoicing software, or check any e-invoice if you are not sure the file is UBL.

Which errors are common?

Missing required fields such as the buyer reference or an electronic address, totals or a VAT breakdown that do not add up, and code values that are not on the allowed lists, such as a unit or VAT category. A UBL file that opens in a viewer can still break these rules, so open and check are separate steps.

Can I turn a UBL file into a readable PDF?

You can open it and print a readable copy, but that is not a format conversion; the XML stays the invoice. To change the file's format, see convert an e-invoice.

Does Klarbon send the invoice?

No. Klarbon checks the file. It is not a Peppol access point and does not send, register or submit invoices.

What happens to my file?

It is sent to Klarbon's servers, validated in memory and deleted after the request. See what happens to my files.

What does it cost?

Free: five checks a day without an account, twenty with a free account, up to 2,000 a day on Pro and Bookkeeper. See prices.

Frequently asked questions

How do I validate a UBL invoice?

Upload the XML file to Klarbon's UBL validator. It checks the invoice against the EN 16931 business rules for UBL, or against the Peppol BIS Billing, XRechnung or NLCIUS rules when the file declares one of those, and reports returned findings with guidance where available.

Which UBL version does the validator support?

UBL 2.1, the syntax EN 16931 binds to. Plain EN 16931 and Peppol BIS Invoice and CreditNote documents are checked. XRechnung and NLCIUS UBL credit notes are not supported checking targets yet. A file in a later UBL version is not automatically an accepted invoice profile.

Is a UBL file that opens also valid?

Not necessarily. Opening shows what the file contains, even when rules are broken. Only a check tells you whether the business rules are met.

Does the validator check Belgian UBL.BE rules?

No. Klarbon does not run the UBL.BE rule set. A Belgian invoice sent over Peppol follows Peppol BIS Billing 3.0, which the validator does check.

Does a valid result mean the invoice will be accepted?

No. A pass means the selected technical rules were met. It does not confirm the tax treatment, the amounts or a recipient's own extra requirements.

Sources

Updated 6 November 2026