Convert CII, UBL and Peppol invoices to XRechnung and back with one REST call. Charged only when the file validates. No document archive is kept.
On this page
The Klarbon XRechnung API converts CII, UBL and Peppol BIS invoices to XRechnung, and XRechnung back to plain UBL or CII, with one REST call. Every file it writes is validated against the rule set selected for the output format before you get it, and a conversion that does not validate costs nothing. Files are processed for the request, without a document archive.
What the API does
POST /api/v1/convert with target=xrechnung writes XRechnung 3.0 in the syntax of your source, UBL or CII.
The answer carries the file and the full validation report, so you see the rule set and every finding.
target=ubl or target=cii turns an XRechnung into the plain EN 16931 syntax.
losses reports fields changed, omitted or assumed when writing the target. It does not include source fields the reader could not carry into the invoice model; compare the result with the original.
What it does not do
XRechnung asks for data some invoices lack, such as a buyer reference. A German public-sector recipient may give you a Leitweg-ID for this field. The API reports what is missing; it never invents it. Klarbon does not send invoices to ZRE, OZG-RE or any other portal. Checking an XRechnung on its own is in beta, see the e-invoice validation API.
Quick start
Each snippet is the same call. The end-to-end test runs these snippets against a local Klarbon server and the real validation engine.
Create a key on your account page and put it in KLARBON_API_KEY. Never put it in the address.
using System.Net.Http.Headers;
using System.Text.Json;
using var http = new HttpClient();
var key = Environment.GetEnvironmentVariable("KLARBON_API_KEY");
http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", key);
var upload = new ByteArrayContent(await File.ReadAllBytesAsync("invoice.xml"));
upload.Headers.ContentType = new MediaTypeHeaderValue("application/xml");
using var request = new HttpRequestMessage(HttpMethod.Post, "https://klarbon.app/api/v1/convert?target=xrechnung") { Content = upload };
request.Headers.Add("Idempotency-Key", "invoice-123456XX-xrechnung");
using var response = await http.SendAsync(request);
using var json = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
var result = json.RootElement;
if (!result.GetProperty("ok").GetBoolean())
{
Console.Error.WriteLine($"{(int)response.StatusCode} {result.GetProperty("error")}: {result.GetProperty("message")}");
return 1;
}
var written = result.GetProperty("file");
await File.WriteAllBytesAsync(written.GetProperty("filename").GetString()!,
Convert.FromBase64String(written.GetProperty("content").GetString()!));
Console.WriteLine($"{written.GetProperty("filename")} written, {result.GetProperty("credits").GetProperty("balance")} credits left");
return 0;
What comes back
The answer to the curl call above, recorded from that run with KoSIT XRechnung test suite, business case 01.01a (CII), Apache-2.0.
Shortened for the page: file.content: base64 cut
{
"ok": true,
"file": {
"content": "PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgi...",
"filename": "123456XX-xrechnung.xml",
"mime": "application/xml",
"bytes": 6867
},
"report": {
"detected": {
"syntax": "cii",
"customizationId": "urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0",
"profile": "xrechnung",
"container": "xml"
},
"ruleset": {
"id": "xrechnung-3.0-cii",
"name": "XRechnung 3.0 (CII)",
"version": "3.0.2"
},
"valid": true,
"engineVersion": "1.0.0",
"durationMs": 45,
"findings": [
{
"ruleId": "BR-DE-TMP-32",
"severity": "info",
"message": "[BR-DE-TMP-32] Eine Rechnung sollte zur Angabe des Liefer-/Leistungsdatums entweder BT-72 \"Actual delivery date\", BG-14 \"Invoicing period\" oder in jeder Rechnungsposition BG-26 \"Invoice line period\" enthalten.",
"location": "/rsm:CrossIndustryInvoice[1]/rsm:SupplyChainTradeTransaction[1]",
"test": "ram:ApplicableHeaderTradeDelivery/ram:ActualDeliverySupplyChainEvent/ram:OccurrenceDateTime or ram:ApplicableHeaderTradeSettlement/ram:BillingSpecifiedPeriod or (every $line in ram:IncludedSupplyChainTradeLineItem satisfies $line/ram:SpecifiedLineTradeSettlement/ram:BillingSpecifiedPeriod)",
"title": "BR-DE-TMP-32",
"what": "[BR-DE-TMP-32] Eine Rechnung sollte zur Angabe des Liefer-/Leistungsdatums entweder BT-72 \"Actual delivery date\", BG-14 \"Invoicing period\" oder in jeder Rechnungsposition BG-26 \"Invoice line period\" enthalten.",
"fix": "",
"link": null,
"officialUrl": null
}
]
},
"losses": [],
"credits": {
"spent": 1,
"balance": 200,
"plan": 0,
"bought": 200
}
}
What it costs
Prepaid API packs, bought by card on your account page: 1,000 calls for €39.00, 5,000 calls for €129.00, 25,000 calls for €449.00, 100,000 calls for €990.00, VAT included, never expiring. Your first key brings 25 free calls once per email address, excluding disposable addresses. Paid calls spend the API balance first, then the same credits as the site. A call that fails costs nothing.
Call
Cost
POST /open
Free, fair use 1,000 a day per account
POST /check
Free within your plan's daily checks (20 a day on the free plan)
POST /convert, POST /make
1 call, only when the written file validates
POST /bank/convert
1 call per started 500 transactions, only when converted
Limits
Files up to 20 MB, PDFs up to 50 pages.
60 requests a minute per key, 120 per account. A per-minute rate-limit refusal carries Retry-After.
Up to 10 keys per account. Idempotency-Key is honoured for 24 hours, so a retry never charges twice.
Errors
Every error is { ok: false, error, message }: a stable code and one plain sentence.
Status
Code
When
401
auth
No key, or an unknown or revoked key.
402
no_credits
The combined API balance and credits cannot cover this call. Nothing was charged; topUpUrl says where to buy.
413
too_large
Over 20 MB or 50 PDF pages.
415
unsupported
A file format the route does not take.
422
invalid
The file could not be read, or the written file did not validate. Not charged.
429
limit
A rate limit or the day's free calls.
503
engine_unavailable
Validation is briefly unavailable. Not charged.
Privacy
Files are processed for the request, without a document archive. Klarbon's application logs carry no file name, no content and no key. The full key is not stored, only an HMAC of it and a short display prefix.