Validate a KSeF FA(3) invoice before sending it

Upload the invoice XML: the validator checks it against the Polish Ministry of Finance's official FA(3) schema and reports every error with its location – before KSeF rejects it.

This page in: Polski

What is checked

The official FA(3) XML Schema, version 1-0E (crd.gov.pl), in force since 1 February 2026.
The schema's occurrence limits (for example the number of invoice lines).
Not checked here: authentication, signature, KSeF number and duplicates – KSeF does that on submission.
Every error with its message and location in the XML.

Rule sets used

Rule set	Published by	Version
KSeF FA(3) (XML schema)	Polish Ministry of Finance	FA3-1-0E

Every rule explained

Every finding in the result links to a page with the official rule text, the severity per rule set and the technical test. The rules of this page:

Checks of this API 1

All 3289 validation rules

Automate the check

The same validator as a REST API: one call with your API key, the result as JSON. The Free plan includes 100 documents a month.

Get a free API key

curl -H "Authorization: Bearer $API_KEY" \
     -H "Content-Type: application/xml" \
     --data-binary @faktura.xml \
     "https://einvoice-api-main-f5141d8.zuplo.app/v1/validate"

Privacy

The file is sent encrypted through our API gateway (Zuplo) to our server in Germany, checked in memory only and discarded after the response. It is neither stored nor logged. To count the validations per day, the gateway uses your IP address; the counter expires after 24 hours. This page sets no cookies. Where you can, use test or anonymised invoices. Details in the privacy policy (German).

Frequently asked questions

Is the validator free?

Yes. You can validate 5 files a day without signing up. For more documents and for validating inside your own software there is the API, with a free plan too (100 documents a month).

Are my invoices stored?

No. The file is checked in memory only, on servers in Germany, and discarded after the response. It never reaches a disk or a log.

Is the result binding?

The validator uses the official rule sets in the version in force and names them in the result. Whether a recipient or a platform accepts the invoice is up to them. Not legal or tax advice.

Does the validator send my invoice?

No. It only validates. Sending through Peppol, the SDI, KSeF or a platform is up to your provider.