Let an assistant open, check and convert e-invoices and bank statements through Klarbon's MCP server, with the same keys, API balance and limits as REST.
This capability is in beta: it works and is tested, and we may still change details.
On this page
Klarbon's MCP server lets an AI assistant or agent open, check and convert e-invoices and bank statements through the Model Context Protocol. It speaks Streamable HTTP at /mcp, uses the same API keys, API balance and limits as the REST API, and does not build a document archive. Listing formats and opening an invoice work without a key.
What the server offers
list_formats and open_invoice, with no key needed.
check_invoice, convert_invoice and convert_bank_statement, with a key as a bearer token.
The file tools take base64 or a public https address and return the same structured results as REST. list_formats takes no file.
What it does not do
It does not send invoices or connect to banks, and it adds no model of its own: your assistant decides when to call a tool. Checking is in beta. Directory listings follow at launch.
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.Net.Http.Json;
using System.Text.Json;
using var http = new HttpClient();
var key = Environment.GetEnvironmentVariable("KLARBON_API_KEY");
http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", key);
http.DefaultRequestHeaders.Accept.ParseAdd("application/json, text/event-stream");
var message = new
{
jsonrpc = "2.0",
id = 1,
method = "tools/call",
@params = new
{
name = "check_invoice",
arguments = new
{
filename = "invoice.xml",
file_base64 = Convert.ToBase64String(await File.ReadAllBytesAsync("invoice.xml")),
},
},
};
using var response = await http.PostAsJsonAsync("https://klarbon.app/mcp", message);
using var json = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
var reply = json.RootElement;
if (reply.TryGetProperty("error", out var error))
{
Console.Error.WriteLine(error.GetProperty("message"));
return 1;
}
var result = reply.GetProperty("result");
if (result.TryGetProperty("isError", out var isError) && isError.GetBoolean())
{
Console.Error.WriteLine(result.GetProperty("content")[0].GetProperty("text"));
return 1;
}
var report = result.GetProperty("structuredContent").GetProperty("report");
Console.WriteLine(report.GetProperty("valid").GetBoolean() ? "valid" : "not valid");
foreach (var finding in report.GetProperty("findings").EnumerateArray())
Console.WriteLine($"{finding.GetProperty("severity")} {finding.GetProperty("ruleId")} {finding.GetProperty("message")}");
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 (UBL), Apache-2.0.
Shortened for the page: result.content[0].text: cut
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.