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For accounting offices

Offline FA(3) validator for accounting offices

Validate every client's FA(3) XML locally — before it reaches KSeF. Invoice data never leaves your computer. PDF, CSV and JSON reports, ready per client.

Download free See pricing

128 validation rules • Runs offline • 0 false negatives in the conformance test (v9)

One rejected invoice costs your office hours

KSeF checks the syntax of the XML file. It does not check whether the invoice complies with the VAT Act. In a test of 256 real invoices, the official KSeF test API accepted 98 documents that break rules it doesn't check.

For an office handling dozens of clients, the error surfaces too late — at the client, during an audit, or in a JPK correction. Every faulty invoice is a call to the client, a re-issue, and the risk of shifting the VAT settlement period.

KSeF Guard checks both — structure and substance — before the file reaches the office. Why validate before sending →

What your office gets

Batch validation

Drag a whole client folder and check all files at once — up to 5,000 per day on Standard, unlimited on Pro. From the command line: ksef-guard validate ./client-invoices/

Client-ready reports

Export to PDF, CSV and JSON — proof the invoices were checked before sending. Pro adds white-label reports with your office's logo.

Full privacy

Validation runs offline. Client files never leave your computer — in line with GDPR data minimisation and confidentiality agreements.

Law-backed proof

Every error has a bilingual explanation and a legal citation (VAT Act, FA(3) brochure) — 128 rules with a documented source.

All 128 rules are free

The free plan validates with every one of the 128 rules — the same as the paid plans. Standard and Pro don't give "more rules." They give what an office needs: throughput, reports, and multiple seats.

Feature Free Standard Pro
Validation rules 128 128 128
Files per day 10 5,000 unlimited
Seats 1 3 10
Report export (PDF, CSV, JSON) — Yes Yes
White-label report with office logo — — Yes
Rule config / YAML profiles — Config Config + YAML
Price €0 €39/mo €89/mo

Net prices. Billing and invoices are handled by DodoPayments (Merchant of Record). Full plan comparison on the pricing page.

How it fits your office

  1. 1

    Download and install — MSI installer or portable ZIP (no admin rights needed).

  2. 2

    Drag a client's invoice folder onto the app — or use the CLI in automation.

  3. 3

    Review the result — which files pass KSeF and which need a fix, with the exact error location.

  4. 4

    Export a report (PDF/CSV/JSON) for the client and fix invoices before sending to KSeF.

Frequently asked questions

Can I validate multiple clients' invoices at once?
Yes. Batch validation checks a whole folder at once. Standard allows 5000 files/day and Pro is unlimited — which is why it suits offices serving many clients.
Is my clients’ data safe?
Yes. Validation runs entirely on your computer. Invoice XML files are never sent to any server or API — they stay on your disk, in line with GDPR data minimisation and confidentiality agreements.
How many seats does a license cover?
Free — 1 seat, Standard — 3 seats, Pro — 10 seats. One license covers the whole office within its seat allowance.
Can I brand reports with my office logo?
Yes. On the Pro plan, PDF reports are white-label — add your own branding and hand them to clients as proof the invoices were checked before going to KSeF.
How is this different from an online validator?
An online validator uploads your file to a third-party server and usually checks 7 to 30 rules. KSeF Guard runs offline and checks 128 validation rules — including 107 obligations KSeF itself does not enforce.
Does KSeF Guard replace my invoicing software?
No. It is a checking tool, not accounting software. It validates finished FA(3) files just before they go to KSeF and tells you what to fix — it does not issue invoices.

KSeF Guard is a technical tool, not tax advice.

Check your clients' invoices before KSeF does

Download KSeF Guard free

Runs offline • All 128 rules in the free plan • No credit card