To validate a Polish KSeF invoice XML file offline, download the current FA(3) XSD from the Ministry of Finance, keep it on your machine, and run an XML Schema validator against both the schema and your XML. Then test rejection with a separate fixture containing one intentional schema violation. Local XSD validation checks structure; it does not submit an invoice to KSeF or confirm that KSeF accepted it.
Get the current official FA(3) schema
Use the Polish Ministry of Finance’s FA(3) structure page as the source for the schema and related documentation, rather than relying on an unofficial mirror. The Ministry says FA(3) replaced FA(2) on 1 February 2026. The FA(3) information sheet identifies system code FA(3), schema version 1-0E, and form variant 3.
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Download the XSD and any files it references, preserving their directory relationships. Store the files locally and point your validator at that local copy. A schema may refer to other schema files; if so, those dependencies must also be available to the validator. Keep a note of the source page and schema version alongside the downloaded files so you can identify which version your checks used.
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An XSD validator checks whether an XML document is well-formed and conforms to constraints expressed in the selected schema, such as element structure, permitted types, and required content. It does not send anything to KSeF, assign an invoice number, or prove that an invoice has been accepted by the service.
The Ministry’s FA(3) guide describes the top-level components as Naglowek, Podmiot1, Podmiot2, Podmiot3, PodmiotUpowazniony, Fa, Stopka, and Zalacznik. Naglowek, Podmiot1, Podmiot2, and Fa are mandatory; Podmiot3, Stopka, and Zalacznik are optional; PodmiotUpowazniony is conditional. The XSD is the appropriate way to test the structural rules encoded in the published schema, but passing it should not be treated as proof that every business or operational detail is correct.
For example, the guide specifies that the purchaser’s Polish NIP belongs in the NIP field within Podmiot2/DaneIdentyfikacyjne. Correct placement matters to whether the invoice is available to that purchaser in KSeF. A file can satisfy structural rules without resolving every question about the invoice’s real-world meaning or workflow.
Run validation against local files
Choose an XML Schema validator available in your environment and explicitly provide both the local XSD and the invoice XML. The exact command varies by validator; the essential inputs are the downloaded FA(3) schema and the XML fixture. Do not point the validator at a third-party schema copy or assume that an XML parser alone performs XSD validation.
- Save the official schema locally. Download it from the Ministry’s FA(3) structure page, along with any referenced schema dependencies.
- Choose a known-good FA(3) sample. Use an invoice XML that is intended to follow the same schema version. Avoid using a sample based on FA(2) or an unspecified schema release.
- Invoke an XSD-aware validator. Configure it to parse the XML and validate against the local FA(3) XSD. Record the validator and schema version when retaining results.
- Inspect the result. A successful result means that the validator found no violation of the selected XSD in that XML. It is not a KSeF submission result.
The guide also notes that DataWytworzeniaFa records the XML generation time; it may differ from P_1 and from the actual delivery time. Its example uses UTC notation with a Z suffix. Treat these fields according to the official guide rather than assuming that timestamps have interchangeable meanings.
Make the validator fail on purpose
Keep the negative test separate from the known-good fixture. First confirm that your valid sample passes. Then make exactly one controlled change that violates a rule in the official XSD—for example, remove an element that the schema requires, or change a value so it violates an applicable type or facet constraint. Save the changed document as a second file and run the same validator with the same local schema.
- Expected test outcome: the deliberately invalid fixture should be reported as invalid by the XSD validation step. Do not assume or report a particular error message without running the chosen validator.
- Keep the change isolated: record what you changed and leave the original fixture untouched. This makes it easier to distinguish the intended failure from an unrelated defect.
- Know the two failure classes: malformed XML fails during parsing because the document is not well-formed; well-formed XML that violates the XSD parses but fails schema validation. A useful negative test should make clear which class it exercises.
If the changed file still passes, check that the validator actually loaded the intended FA(3) XSD, that the altered rule is enforced by that schema, and that the validator is running schema validation rather than XML parsing alone. If the original sample fails, confirm that it is an FA(3) document and that the local schema and any dependencies were downloaded correctly.
Use KSeF’s test environment for the end-to-end check
Local validation and a KSeF workflow test answer different questions. The Ministry’s KSeF 2.0 test application is integrated with the test API environment and supports FA(3) invoice workflows. It requires fictitious data, and actions in that environment have no legal effects. Use it when you need to test interactions with the service, rather than treating a local XSD pass as an end-to-end acceptance check.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Do not confuse local validation with regulated offline issuing
Here, “offline validation” means checking XML locally without contacting KSeF. It is separate from the tax procedures that use “offline24” or “offline – KSeF unavailability” to describe ways of issuing invoices when the service is unavailable or under specified conditions.
The Ministry’s offline24 procedure says to use the applicable structure—FA(3) from 1 February 2026—and submit an invoice no later than the next business day after issue in the ordinary case. The page describes different handling for a KSeF failure or total failure before submission.
For the announced KSeF-unavailability mode, the Ministry’s offline procedure during KSeF unavailability describes an ordinary deadline of no later than the next business day after the unavailable period ends, a separate seven-business-day deadline after an announced failure, and non-submission for total failure. These are distinct conditions, not one universal deadline; consult the official procedure that applies to the situation.
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