What Contalia is and what it's for

If you're self-employed or have a small business in Spain, 2025 and 2026 have brought a new word that you can't ignore: VeriFactu. The Tax Agency has changed the rules for issuing invoices, and suddenly the old Excel spreadsheet or outdated program is no longer valid. Contalia was created just for this purpose: a desktop accounting and invoicing program for Windows, designed for self-employed individuals and small businesses, which complies with VeriFactu without requiring you to be an expert in regulations or pay a fortune.

In this article, I'll explain what VeriFactu is and how it affects you, what specific problem Contalia solves, how it works internally, and who it's suitable for. Without unnecessary technical jargon: the idea is to help you understand why this software exists and what it takes off your plate.

What is VeriFactu and how does it affect you

VeriFactu is, in a few words, the name given to the new framework that regulates invoicing systems in Spain, within the anti-fraud law. Its objective is clear: to prevent invoices from being manipulated afterwards. Until now, it was technically possible to issue an invoice, save it, and then "retouch" or delete it without leaving a trace. The new regulations aim to put an end to this.

What does this imply in practice for invoicing software? In broad terms:

• Unalterable records. Each invoice generates a record that cannot be modified or deleted without leaving a record. What is issued, remains.
• Invoicing chain. Each record is linked to the previous one, forming a chain. If someone tries to remove or alter an invoice in the middle, the chain would break and be noticeable. It's the same integrity principle used in other trust systems.
• Traceability and compliant format. Invoices must follow a specific format and be traceable, so that the Tax Agency can verify them.
• Impossibility of using "dual-use" software. The days of programs that allowed keeping two separate accounting records ("A" and "B") are over.

The consequence for you is direct: your invoicing software must comply. It's not optional, it's not a recommendation. And that leaves out a lot of improvised solutions (spreadsheets, Word templates, outdated programs).

The problem: complying without going broke or crazy

Here's the real problem, and it's not the regulation itself, but what comes after. When a self-employed individual or a small business discovers they have to comply with VeriFactu, they're faced with two bad options:

1. Expensive solutions. Complete accounting suites, designed for accounting firms or large companies, with a monthly cost that's disproportionate for a self-employed individual and with thousands of functions they'll never use.
2. Complex solutions. Programs that technically comply, but are so cumbersome that you need a course to issue an invoice. For someone who just wants to invoice their clients and get on with their work, it's a burden.

The result is the feeling of being trapped: either you pay too much, or you struggle with a complicated tool, all to comply with an obligation that doesn't generate a single euro of income. It's pure cost and pure hassle.

Contalia addresses this gap: complying with VeriFactu while being simple on the outside and rigorous on the inside, at a reasonable cost for those who aren't a large company.

What is Contalia

Contalia is a desktop accounting and invoicing program for Windows, aimed at self-employed individuals and small businesses, compliant with the VeriFactu regulation of the Tax Agency. The ideas that define it are three:

1. Data model oriented towards compliance. It's not invoicing with compliance "added on" later, but designed from the start around the chain and traceability required by the regulation. The rigor is in the foundation, not a patch.
2. Built on .NET 10 and Blazor. A modern technological base that allows for a single code base and a solid, maintainable application.
3. Focus on small businesses and self-employed: simple on the outside, rigorous on the inside. On the inside, it does what the law requires with all the rigor; on the outside, it tries to show you only what you need to invoice without headaches.

It's, in essence, the tool I would have liked to find for a self-employed individual: one that complies with the law without making compliance a project in itself.

How Contalia complies with VeriFactu

Without getting into legal jargon, this is how Contalia addresses the requirements:

• Invoicing chain. Each invoice you issue is linked to the previous one, forming that chain of integrity that the regulation demands. It's the technical guarantee that the sequence hasn't been manipulated.
• Unalterable record. What's issued is saved in a way that can't be altered without leaving a record. This is exactly what the anti-fraud law seeks.
• Compliant export. Data can be exported in the correct format, so that compliance isn't just "inside" the program, but also serves the Administration.

All this lives in a compliance-oriented domain layer, which is the technical way of saying that the logic of "how invoices should behave according to the law" is well separated and well cared for, not mixed in any way with the rest of the program.

Why a desktop application for Windows

In a world where everything is moving to the cloud, creating a desktop program may seem counterintuitive, but it makes sense for this case:

• Your accounting data, on your computer. For many people, accounting is something they prefer to keep on their own computer and not on a third party's server. A desktop application provides that peace of mind.
• It works without depending on a perfect internet connection. You can invoice even if the internet fails.
• Windows is the real environment of most small businesses and self-employed individuals in Spain. Taking the tool to where the user is, rather than forcing them to change habits, is part of the "simple on the outside" approach.

How it works internally

For those interested in the technical side: Contalia is built on .NET 10 and Blazor, with persistence in PostgreSQL.

• .NET 10 is a robust, fast, and very suitable platform for business applications where reliability matters —and in accounting, it matters a lot—.
• Blazor allows building the interface with a single code base, which translates into more coherent and maintainable development.
• PostgreSQL as a database provides solidity and guarantees for something as delicate as accounting records: it's a serious relational database, just what's needed for a domain with so many relationships and such a need for integrity.

This choice isn't casual: when what's at stake is legal compliance and the integrity of someone's tax data, you don't want shortcuts. You want a technological base that can withstand it.

Real use cases

• The self-employed individual who invoices their clients. Needs to issue compliant invoices without setting up an accounting firm within their computer. Contalia provides just that.
• The small business. A handful of employees, regular invoicing, and the obligation to comply with VeriFactu without contracting an expensive suite.
• Those coming from Excel or an old program. Know that what they used is no longer valid and need to move to something that complies, but without a brutal complexity leap.
• The professional who values having their data locally. Prefers their accounting to live on their computer and not in a provider's cloud.

Who it's aimed at

Contalia is designed for self-employed individuals and small businesses that must comply with VeriFactu and want to do so without going broke or complicating their lives. It doesn't aim to compete with large accounting suites for accounting firms and large companies; its place is with the professional or small business that needs to invoice well, comply with the law, and get on with their work. If you recognize yourself in this profile —and in Spain, there are hundreds of thousands—, Contalia is made for you.

Contalia versus alternatives

Let's put the options on the table:

• Sticking with Excel or templates. No longer complies. It's directly giving up being a legal option.
• A large accounting suite. Complies, but is usually expensive and excessive for a self-employed individual, with thousands of functions that will never be used.
• A complex program "that complies". Technically correct, but with a learning curve that steals time and patience.
• Contalia. Bets on the middle ground: rigorous compliance with VeriFactu, in a desktop application designed so that the self-employed individual or small business can use it without headaches, at a reasonable cost.

The right choice depends on your size and needs, but if you're small and what you want is to comply without suffering, that's exactly the gap Contalia fills.

Common mistakes when choosing invoicing software

• Leaving it for the last day. Adapting to VeriFactu in a hurry is a recipe for mistakes. Better to switch to a compliant tool with time.
• Paying too much "just in case". Contracting a huge suite when all you need is invoicing is throwing money away each month.
• Choosing the cheapest option without checking if it complies. A program that doesn't comply with VeriFactu is useless, no matter how cheap it is. Compliance is the minimum requirement, not an extra.
• Forgetting where your data is. It's good to know if your accounting lives on your computer or on someone else's server, and to decide with knowledge.

Frequently asked questions

Does Contalia comply with VeriFactu? Yes, it's designed from its base to comply with the regulation, with invoicing chain, unalterable record, and compliant export.

Is it for large companies? Not especially. Its focus is on self-employed individuals and small businesses that want to comply without complications.

Are my data in the cloud? It's a desktop application for Windows, designed so that your accounting data lives on your own computer.

Do I need advanced accounting knowledge? The philosophy is "simple on the outside": comply with the rigor that the law demands without forcing you to be an expert to issue an invoice.

Migrating to Contalia: how the change is

One of the biggest barriers to changing invoicing software is the fear of change itself: "what if I lose my data?", "what if I don't understand it?". It's a reasonable fear, and that's why Contalia's philosophy —simple on the outside— aims directly at this. The idea is that switching isn't a leap into the unknown, but a natural step: start issuing your invoices according to the regulation without having to relearn everything.

The well-made change consists of familiarizing yourself calmly, starting to invoice with the new tool, and leaving the old method behind, little by little. It's not setting up an accounting department; it's replacing a piece that no longer works (the old Excel, the outdated program) with another that complies and takes problems away. The sooner you take this step, the more familiar you'll be when the obligation becomes urgent.

What your business gains beyond complying with the law

It's easy to see VeriFactu as just a nuisance, but switching to a serious invoicing software has benefits that go beyond avoiding a fine:

• Order. All your invoices in one system, not scattered between folders, emails, and your head. When it's time to do accounts or pass something to the accounting firm, you have it localized.
• Professional image. Compliant and well-presented invoices convey seriousness to your clients. It says a lot about a business how it invoices.
• Fewer errors. A system that chains and validates reduces the typical errors of "doing it by hand": duplicates, broken numbering, poorly copied data.
• Time. Every minute you don't struggle with invoicing is a minute for your real work. Well-resolved bureaucracy is noticeable in your peace of mind.
• Peace of mind in case of an inspection. Knowing that what you issue complies with the regulation and is traceable takes a weight off your shoulders. It's no small thing.

In other words: the obligation is the push, but the prize is stopping to manage your invoicing with fear and disorder.

The calendar: why it's better not to wait

With regulatory changes, it always happens the same: people leave it for the last minute and then rush and stress. Adapting to VeriFactu isn't something you want to do in a hurry, because changing invoicing software involves getting used to it, migrating your data, and getting comfortable.

Switching to a compliant solution like Contalia with time has a clear advantage: you do it calmly, test, familiarize yourself, and when the obligation becomes urgent, you're already ready and calm while others rush. In regulatory compliance, anticipation always costs less than urgency. And, honestly, it's less stressful.

Current status

Contalia is a product: a desktop application for Windows built on .NET 10, Blazor, and PostgreSQL, with VeriFactu compliance at its core. From this base, the natural evolution involves expanding the management functions that the daily life of a self-employed individual or small business requires, always maintaining the balance between regulatory rigor and simplicity of use.

In summary

Contalia solves an obligation that millions of self-employed individuals and small businesses in Spain have: issuing invoices compliant with VeriFactu, without paying too much for a huge suite or struggling with an impossible program. It does so as a desktop application for Windows (.NET 10, Blazor, PostgreSQL) with compliance in its foundation —invoicing chain, unalterable record, compliant export— and a clear philosophy: simple on the outside, rigorous on the inside.

If you must comply with VeriFactu and are looking for a tool tailored to your needs, check out the full Contalia profile. And if you need software adapted to your specific business, let's talk: building tools that solve real problems is exactly what I do.