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Draft, under review

Zero MCP server (Zéró Számla)

Beállítás

Minden AI-asszisztensben ugyanaz a menet: adj hozzá egy egyéni (távoli) MCP-csatlakozót ezzel a címmel: https://mcp.zeroszamla.hu. Utána jelentkezz be a megnyíló Zero-oldalon; ez egyben a regisztráció is.

  • Claude: egyéni csatlakozó a fenti címmel. Ellenőrzés alatt
  • ChatGPT: egyéni csatlakozó (app) a fenti címmel. Ellenőrzés alatt
  • Le Chat: egyéni MCP-csatlakozó a fenti címmel. Ellenőrzés alatt
  • Grok: egyéni MCP-csatlakozó a fenti címmel. Ellenőrzés alatt

Néhány AI-asszisztensnél a csatlakozóhoz fizetős csomag kell. A részletes, angol nyelvű technikai leírás lent olvasható.

What Zero is

Zero is a Hungarian e-invoicing service that you operate entirely from your own AI assistant through a remote MCP server. Zero itself runs no AI: it provides the legally required, deterministic core (validation, gap-free numbering, NAV Online Számla submission, PDF seal, 8-year write-once archive, audit log) and exposes it as MCP tools.

Who it’s for

  • Hungarian sole traders (egyéni vállalkozó) and small businesses that issue invoices and must report them to NAV (the Hungarian tax authority) through Online Számla.
  • People who already use Claude, ChatGPT, Le Chat or Grok and want to invoice by asking their assistant instead of using a separate invoicing app.
  • Accountants of those businesses (read access and exports via invitation).

Not a fit: issuers outside Hungary (Zero only serves Hungarian issuers, so NAV reporting applies to every invoice), or anyone who needs a classic point-and-click web dashboard.

Cost

  • Free for businesses, as a written commitment. No subscription, no paywall, no ads, no data selling. The commitment is backed by a data-export guarantee (see get_full_export: the full invoice archive as one ZIP, no count limit, no fee).
  • There are no paid tiers and no per-invoice fees for businesses.

Connect

Item Value
MCP server URL https://mcp.zeroszamla.hu (root; https://mcp.zeroszamla.hu/mcp is an equivalent alias)
Transport Streamable HTTP, stateless, JSON responses. POST only; GET/DELETE on /mcp return 405. No server-initiated SSE.
JSON-RPC batching Not supported (removed from the MCP spec in 2025-06-18). Send one message per request.
Auth OAuth 2.1, authorization code + PKCE (S256), public clients (token_endpoint_auth_method: none)
Discovery Unauthenticated requests get 401 with WWW-Authenticate: Bearer resource_metadata="https://mcp.zeroszamla.hu/.well-known/oauth-protected-resource" (RFC 9728)
Authorization server metadata https://api.zeroszamla.hu/.well-known/oauth-authorization-server (RFC 8414)
Dynamic Client Registration Yes, RFC 7591: POST https://api.zeroszamla.hu/oauth/register (limited to 10 registrations per IP per hour)
Token lifetimes Access token 1 hour; refresh token 30 days, rotated on use; every grant expires after 90 days at most, then the user re-authorizes
Sign-up The OAuth consent page is also the sign-up and login. No separate account creation step.
Static API keys None. OAuth is the only way in.

Scopes (requested at consent): invoice:read, invoice:write, invoice:issue, invoice:cancel, partner:read, partner:write, connection:read, connection:write, stats:read, webhook:read, webhook:write, accountant:manage, expense:read (inbound invoices from NAV), expense:write (start the inbound sync), audit:read, system:ping.

Per-client setup

In every client the flow is the same: add a custom (remote) MCP connector with the server URL above, then sign in on the Zero consent page that opens.

  • Claude: add a custom connector with https://mcp.zeroszamla.hu. Ellenőrzés alatt
  • ChatGPT: add a custom connector / app with https://mcp.zeroszamla.hu. Ellenőrzés alatt
  • Le Chat (Mistral): add a custom MCP connector with https://mcp.zeroszamla.hu. Ellenőrzés alatt
  • Grok: add a custom MCP connector with https://mcp.zeroszamla.hu. Ellenőrzés alatt

Zero does not rely on MCP resources or prompt templates, only on tools, so clients with tools-only MCP support work.

Capabilities

Tool names below are the ones tools/list returns. Every tool carries title, readOnlyHint and destructiveHint annotations. Tools run only inside the signed-in user’s own account (tenant isolation is enforced in the database).

Legend: RO = read-only. Destructive = destructiveHint: true. Confirmation: 2-step = preview + prepare_token, then confirm=true; confirm = requires confirm=true; - = none. Idem. = accepts idempotency_key.

Invoices

Tool What it does RO Destructive Confirmation Idem.
list_invoices List invoices, filter by status (draft, issued, failed, cancelled, queued) or free text yes no - -
get_invoice Get one invoice by ID yes no - -
create_invoice_draft Create a draft (not yet a legal document) no no - yes
update_invoice_draft Edit a draft (draft state only) no no - -
delete_invoice_draft Delete a draft (draft state only) no yes confirm -
issue_invoice Issue a draft: creates the real invoice, numbers it, reports to NAV. Reversible only by cancellation. no yes 2-step yes
resubmit_invoice Resubmit a failed invoice no yes 2-step yes
cancel_invoice Cancel (storno) an issued invoice, reason required no yes 2-step yes
get_invoice_pdf Download URL of the invoice or storno PDF yes no - -
get_invoice_provider_status NAV submission status of an invoice yes no - -
get_document_chain Full document chain (original, modifications, storno) yes no - -
send_payment_reminder Send a polite payment reminder e-mail for an unpaid invoice no no - yes
Tool What it does RO Destructive Confirmation Idem.
get_invoice_link Public live invoice link, optional QR code (issued invoices only) no no - -
revoke_invoice_link Invalidate a live link and issue a new one no yes confirm -
create_collection_link One link to a set of invoices (period or list), e.g. for the accountant; expires (default 90 days, max 730) no no - -
list_collection_links List collection links yes no - -
revoke_collection_link Revoke a collection link no yes confirm -

Customers (partners)

Tool What it does RO Destructive Confirmation Idem.
list_partners List customers yes no - -
get_partner Get one customer yes no - -
create_partner Create a customer no no - -
update_partner Edit a customer no no - -
delete_partner Delete a customer no yes confirm -
lookup_taxpayer Look up a Hungarian taxpayer at NAV by the first 8 digits of the tax number (uses the user’s own NAV connection) yes no - -
Tool What it does RO Destructive Confirmation Idem.
sync_inbound_invoices Pull supplier invoices reported to NAV about this business (max 92-day range; skips ones already stored) no no - built-in
list_inbound_invoices List pulled inbound invoices (max 500 rows) yes no - -

Exports and evidence

Tool What it does RO Destructive Confirmation Idem.
get_full_export Entire archive as one ZIP (all PDFs + structured data + manifest); returns a download path, not the content yes no - -
export_invoices_csv CSV export for the accountant (summary or line level) yes no - -
export_invoices_aea NAV audit data export (AEA XML) for a date or number range yes no - -
verify_invoice_evidence Check one invoice’s 8-year evidence chain (Merkle batch, timestamp, renewal chain) yes no - -
get_stats Totals: issued, drafts, failed, cancelled yes no - -
get_invoice_stats Invoice statistics with daily breakdown yes no - -

Business, team and accountants

Tool What it does RO Destructive Confirmation Idem.
list_memberships Businesses this account can manage (owner, admin, member, accountant) yes no - -
update_business_settings Invoice number prefix, automatic payment reminders on/off (off by default) no no - yes
invite_member Invite a colleague or accountant by e-mail (no access until accepted) no no - -
set_accountant_issue_permission Allow or deny an accountant to issue invoices for the business no no - yes
revoke_member Revoke a membership no yes confirm -
list_accountants Accountant connections of the business yes no - -
invite_accountant Invite an accountant (link valid 14 days) no no - -
list_accountant_clients For a signed-in accountant: active clients yes no - -

System

Tool What it does RO Destructive Confirmation Idem.
ping Connection test: is the token valid, which scopes it has yes no - -
explain_error Machine-readable error catalog: description, next step, retryable yes no - -
list_connections Configured connections (metadata only, never keys) yes no - -
list_providers Capability matrix of the invoicing backends yes no - -

Invoice data supported

  • Document types: e-invoice (default), paper, pro forma (díjbekérő), advance invoice; storno via cancel_invoice; simplified invoice (Áfa tv. 176. §) via a flag.
  • Currencies: HUF, EUR, USD.
  • VAT: any rate in percent, plus exemption codes AAM, TAM, KBAET, EAM, EUFAD37, FAD and an explicit 0% code (a real 0% supply is not the same as an exemption; omitting the code sends 0% as AAM).
  • Payment methods: bank transfer, cash, card.
  • Buyers: Hungarian tax number, EU VAT number for foreign buyers, or private individuals.
  • Delivery: the invoice e-mail to the customer is on by default (can be switched off per invoice); the link and QR code are always returned to the conversation as well.
  • Invoice language: Ellenőrzés alatt

Safety model

Zero does not trust the AI that calls it. It accepts structured input and validates every write on the server.

  1. Preview before anything irreversible. issue_invoice, resubmit_invoice and cancel_invoice are two-step. The first call (no prepare_token) executes nothing and returns a preview plus a prepare_token. The agent shows the preview to the user and asks for explicit approval, then calls again with confirm=true and the token.
  2. The token is bound to the user, the tool, the document and a fingerprint of its content. It expires after 10 minutes. If the document changed after the preview, the call fails with prepare_invalid and a new preview is needed.
  3. Other destructive tools (deleting drafts or customers, revoking links or members) require confirm=true.
  4. Idempotency. Writes run inside an idempotency wrapper. Pass your own stable idempotency_key (for example monthly-fee-2026-10) on scheduled or retried runs: a repeated call returns the stored result instead of creating a second invoice. Same key with different content is rejected as a conflict, not silently overwritten.
  5. Secrets never go through the chat. NAV technical-user credentials are entered only on a secure Zero web page. Tools that list connections return metadata, never keys. Authorization and cookie headers are stripped before the MCP layer.
  6. Returned data is data. Tool results containing invoice or customer text are marked as user data, not instructions.
  7. Automation. For unattended runs a standing authorization is planned. Ellenőrzés alatt

Compliance

  • NAV Online Számla: every issued invoice is reported to NAV (API v3.0). NAV’s receipt is the primary independent proof of issue time.
  • Test or live NAV mode per business: a business can run against NAV’s test system before going live. Ellenőrzés alatt
  • PDF seal: each issued PDF gets a PAdES signature (RSA-3072, SHA-256) with an embedded RFC 3161 timestamp. This is an advanced-level electronic seal, not a qualified one, and Hungarian law does not require a qualified signature for e-invoices.
  • Archive: issued PDFs are stored byte-identical in object storage with WORM (COMPLIANCE mode) retention of 8 years, the Hungarian retention period.
  • Audit log: writes are logged (event-sourced audit log); data-access log retained 2 years.
  • Hosting: data at rest in the EU (Scaleway, Paris region fr-par). Network edge, DNS and WAF: Cloudflare (a US company). We do not claim full EU sovereignty.
  • GDPR: the operator is a US company with an EU representative under GDPR Art. 27 (Euverify Limited, Ireland). Transfers outside the EU rely on the European Commission’s standard contractual clauses; details in the privacy notice (https://zeroszamla.hu/adatvedelem). Ellenőrzés alatt

Limits and errors

  • Rate limits: 120 requests per minute per OAuth grant; 100 requests per minute per IP (default). Exceeding them returns HTTP 429 with Retry-After.
  • Request size: up to 12 MB per request.
  • Invoice limits: 1 to 200 lines per invoice; quantity up to 1 000 000; comment up to 2000 characters; list results up to 100 invoices (500 inbound invoices) per call.
  • Monthly issue cap: a per-account monthly cap exists as a cost safety valve and is off by default. If enabled and reached, tools return monthly_issue_limit_reached.
  • Error model: tool errors carry a stable code. Call explain_error with the code (or without one for the full catalog) to get a description, the next step and whether it is retryable. Main codes: validation_error, not_found, forbidden, confirm_required, prepare_invalid, issue_failed, cancel_failed, sync_failed (retryable), taxpayer_failed (retryable), internal (retryable).
  • Transport errors: 401 with OAuth discovery header when unauthenticated or the token is invalid; 400 for JSON-RPC batches; 405 for non-POST.

Data and privacy

  • No server-side AI. Zero sends your data to no AI model. The only AI involved is the one you chose and connected. Its own data policy applies to what you type into it.
  • No ads, no data selling.
  • Your data, exportable at any time: get_full_export returns everything as a ZIP. Before an account is deleted a full export is required, and the archive stays retrievable afterwards with a one-time code sent to the account’s e-mail address.
  • Tenant isolation: every request runs only in the signed-in user’s account; the database enforces row-level security.
  • Minimized lists: list tools return trimmed rows to keep data out of the chat; full details come from get_* tools on request.

Status

  • Zero is in pre-launch as of 25 October 2026. Ellenőrzés alatt
  • Planned maintenance will be announced through a service_status tool. Ellenőrzés alatt
  • Status page: Ellenőrzés alatt

Contact

  • https://zeroszamla.hu/llms.txt (index for AI tools)
  • https://zeroszamla.hu/llms-full.txt (full text)
  • https://mcp.zeroszamla.hu/.well-known/oauth-protected-resource (RFC 9728)
  • https://api.zeroszamla.hu/.well-known/oauth-authorization-server (RFC 8414)
  • MCP tools/list on https://mcp.zeroszamla.hu (after OAuth) is the authoritative tool list.
  • OpenAPI / MCP manifest (/.well-known/mcp.json or similar): none published. Ellenőrzés alatt