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Terms of use of the mul.tax AI assistants

Version 1.0 · in force since 24 September 2026

1. Who provides the service

2. What the assistants are

They are conversational tools based on a general-purpose artificial intelligence model (Claude, by Anthropic PBC) that mul.tax configures with its own instructions and knowledge. Currently: Administrative appeals and AEAT, IAE – CNAE classification and VAT: returns to carry forward or refund.

AI systems can make mistakes: they may misquote a rule, miscalculate a deadline or propose an unsuitable route. That is why everything they generate is a draft that a qualified person must review. All content they generate is labelled as AI-generated.

3. Two plans

3.1. Professionals. People acting in the course of a professional activity in tax, legal, accounting or administrative advice (tax advisers, gestores, lawyers, economists, labour consultants and the like) can access directly. On accessing, the user declares:

1. that they act as a professional and not as a consumer;
2. that they will review all generated content before using it, filing it with any authority or delivering it to a client;
3. that they are solely responsible to their clients for the content they finally use.

3.2. Individuals and companies. Anyone can send their case through the form. The AI prepares an internal draft that is not shown to the user. A mul.tax professional reviews, completes or discards it and sends a fixed quote. The service (the reviewed document) is only provided if the person accepts the quote.

4. Scope and limits

• The assistants cover administrative and economic-administrative proceedings in tax matters. They do not cover contentious-administrative court proceedings, criminal proceedings (including possible tax offences) or court representation. If your case requires it, we will tell you and recommend that you see a lawyer.
• We do not guarantee any result. The success of an appeal depends on the authority or court.
• Deadlines given by the AI must always be checked against the actual date of notification.
• Rules and administrative criteria change: the assistants' knowledge is updated regularly, but may not reflect very recent changes.

5. Prices, payment and invoice

• Professionals: pack of 5 cases (€29 + VAT, valid 12 months) or monthly subscription (€49 + VAT, up to 40 cases a month, cancellable at any time with effect at the end of the paid period). A “case” is a conversation of up to 15 messages on one matter. A limited free trial is available.
• Individuals and companies: fixed quote for each case, VAT included, expressly accepted before payment.
• Payment is by card through Stripe. Vilafant Gestió, S.L. issues the corresponding invoice.
• Free codes that mul.tax gives to specific people are personal and non-transferable, expire every 15 days and may be revoked.

6. Right of withdrawal (consumers)

If you are a consumer, you have 14 calendar days to withdraw from the contract without giving a reason. However, when accepting the quote you can expressly ask us to start work before this period ends; in that case, under article 103.a of the consolidated text of the Spanish General Consumer and User Protection Act, you will lose the right of withdrawal once the service has been fully performed (delivery of the reviewed document), and if you withdraw earlier you must pay the proportional part of the work done. To withdraw, write to josep@mul.tax.

Professionals have no right of withdrawal.

7. Liability

• Professionals: the service is a support tool. The professional is responsible for reviewing the content and for how it is used. The liability of Vilafant Gestió, S.L. towards professionals is limited to the amount actually paid for the service in the 12 months before the event giving rise to it, except in cases of wilful misconduct or gross negligence.
• Individuals and companies: Vilafant Gestió, S.L. is liable for the work reviewed and delivered by its professional in accordance with applicable rules. Nothing in these terms limits the rights the law grants to consumers.
• No plan includes filing the document on your behalf, unless we expressly agree so in writing.

8. Acceptable use

The service may not be used for unlawful purposes, to try to obtain undue refunds or tax benefits, to enter third parties' data without a legal basis, to try to extract the assistants' instructions or limits, or in an automated or mass manner. We may suspend access if these terms or the model provider's usage policy are breached.

9. Personal data

Data processing is governed by the privacy policy. When a professional enters client data in the chat, Vilafant Gestió, S.L. acts as data processor on their behalf under the terms of Annex I, which forms part of these terms. The browser automatically replaces tax IDs, IBANs, emails and phone numbers with placeholders before sending the text; even so, we recommend not entering identifying data that is not necessary.

10. Intellectual property

The assistants' instructions, knowledge and design belong to Vilafant Gestió, S.L. You may freely use the drafts you obtain for your cases.

11. Changes and term

We may amend these terms; changes will apply to cases started after their publication. Subscriptions may be cancelled at any time.

12. Complaints, governing law and jurisdiction

You can send any complaint to josep@mul.tax; we respond within 30 days at most. If you are a consumer, official complaint forms are available to you and you can go to the Catalan Consumer Agency (Agència Catalana del Consum) or the municipal consumer information office. These terms are governed by Spanish law. For consumers, the courts of their place of residence have jurisdiction; for professionals, those of Vilanova i la Geltrú.

Annex I. Data processing agreement for professionals (art. 28 GDPR)

1. Purpose: Vilafant Gestió, S.L. (processor) processes on behalf of the professional (controller) the data the latter enters in the chat, solely to generate the requested answers.
2. Term: that of each conversation. The history is deleted automatically within 24 hours at most.
3. Data and data subjects: identification, tax and financial data of the professional's clients. The professional must not enter special categories of data (health, etc.).
4. Instructions: the processor handles the data only on the controller's documented instructions, namely these terms and the use of the chat.
5. Confidentiality: authorised persons are bound by a duty of confidentiality.
6. Security: encryption in transit (HTTPS), pseudonymisation in the browser of tax IDs, IBANs, emails and phone numbers, minimal retention and restricted access.
7. Authorised sub-processors: Anthropic PBC (AI model; US, with European Commission standard contractual clauses) and Cloudflare, Inc. (infrastructure; with standard contractual clauses). The processor will give advance notice of any change so that the controller can object.
8. Data subject rights, security breaches and assessments: the processor will assist the controller and notify it without undue delay of any security breach affecting its data.
9. End of the engagement: data is deleted automatically when the conversation ends (24 hours at most), with no copy kept.
10. Audit: the processor will make available to the controller the information needed to demonstrate compliance with these obligations.