Your data, in an open format

katlab invoicer keeps nothing on a server, and it doesn’t lock you in either. If this site disappeared tomorrow, you would lose nothing.

Three ways your data outlives this website

1. Offline copy. Download the complete app (about 1 MB). Unzip it, run python3 -m http.server in the folder and open http://localhost:8000 — it works without internet and never contacts katlab.
2. Every PDF carries its data. Each PDF you download contains the document as an attached invoice.json file. Drop the PDF onto the Documents page (here or in the offline copy) and it comes back — with its number, lines, client and payments.
3. Backups in plain JSON. Settings → Backup → Download backup saves everything in the format below, readable by any program.

Backup file (schemaVersion 2)

{
  "app": "katlab-invoicer",
  "schemaVersion": 2,
  "exportedAt": "2026-09-23T10:00:00.000Z",
  "data": {
    "meta":       [{ "id": "activeBusinessId", "value": "…" }],
    "businesses": [Business],
    "clients":    [Client],
    "products":   [Product],
    "docs":       [Document],
    "payments":   [Payment]
  }
}

Conventions

• Every record has a string id and an ISO updatedAt. Restoring merges by id: newer records win and issued documents are never replaced by drafts.
• Money and quantities are decimal strings ("1250.50", "1.5") — never floating-point numbers. Payment amounts are integer strings in minor units ("125050" = 1,250.50).
• Dates are YYYY-MM-DD strings with no time zone.

Document

• type: invoice, quote, proforma, credit_note, receipt, delivery_note, purchase_order · status: draft, issued, void
• number, seq, seqKey (the counter and year it was issued under), issueDate, supplyDate, dueDate, validUntil, issuedAt
• seller and client: snapshots of name, address, country, VAT ID and bank details at the time of issue
• currency, fxRate, fxSource, fxDate, docLang, secondLang, priceMode (net/gross), rounding (doc/line)
• lines[]: name, description, qty, unit, unitPrice, discount {type: pct|abs, value}, tax {id, rate, category, label} — category codes follow EN 16931 (S, Z, E, AE, K, G, O)
• docDiscount, charges[] (label, amount, tax), legalNotes[], customFields[], notes, footer, payment (IBAN, reference, QR standard), theme
• Optional: refDoc (credit note / receipt / conversion source), advance and finalOf (advance invoices), acceptance (quote acceptance), recurrence (repeat schedule)

Totals are not stored — they are always recomputed from the lines, so a backup can never contain totals that disagree with its items.

Payment, Client, Product

• Payment: documentId, date, amountMinor, method, note
• Client: name, address, country, vatId, email, docLang, currency
• Product: name, description, unit, unitPrice, taxRateId

Data inside each PDF

PDFs contain an embedded file invoice.json (relationship Source) with {"app": "katlab-invoicer", "kind": "document", "schemaVersion": 2, "doc": Document, "payments": [Payment]}. Most PDF readers show it under Attachments.

Share links

Share links put the document after the # in the address — the part browsers never send to a server. Format: v1.z.<data> (compressed), v1.e.<salt>.<iv>.<data> (AES-GCM encrypted with a key derived from your password using PBKDF2-SHA256, 600,000 iterations), or v1.r.<data> (uncompressed, for older browsers).

Frequently asked questions