involy. Turning my own problem into a free tool
How involy came about, what the tools do, why everything runs locally in the browser and what the XRechnung export is all about.
involy came out of my own need. As a self-employed person I wanted to know what I owed the tax office, to document income and expenses cleanly, to calculate input VAT correctly and to file the whole thing at Elster myself. I would rather build tools like this myself than take out a subscription or learn someone else's software.
At some point this turned into the question of whether other self-employed people were missing the same thing. Since then involy has been a small public site with tools that I keep maintaining and extending when needed.
The tools
Every tool works on its own. Master data like name, address and tax number is entered once and is then available everywhere.
The invoice tool creates legally compliant invoices under § 14 UStG. Five templates, net or gross input, automatic VAT calculation, PDF export and XRechnung XML following EN 16931.
The EÜR and input-VAT tool is aimed at standard-taxation businesses. Incoming invoices, income and recurring expenses are collected in one register, input VAT is calculated under § 15 UStG and a complete cash-basis profit statement with the VAT amount due is produced.
The small-business tool documents income and expenses without VAT, with a tracker for the current revenue thresholds under § 19 UStG.
Why everything runs locally in the browser
involy has no backend. All data stays exclusively in local browser storage, no server, no cloud, no tracking. The reason is simple: tax numbers, customer data and invoice amounts have no business on someone else's servers.
The downside is known. Anyone who clears their browser storage or switches devices loses their data. That is why every tool has a JSON export as a backup that you should pull regularly.
XRechnung and the e-invoice obligation
I built in the XRechnung export because the legal direction was foreseeable. I tested the export against several XML validators, all of them accepted and confirmed the format.
Since 1 January 2025 all companies in Germany are required to receive electronic invoices in B2B. The format has to follow the European standard EN 16931. A PDF has not counted as a proper e-invoice since then.
For the obligation to send there are staggered deadlines. Anyone with more than 800,000 euros in revenue in 2026 has to send in the XRechnung or ZUGFeRD format from 2027. For everyone else the deadline runs until the end of 2027, and from 2028 the obligation applies to all domestic B2B sales without exception.
For the self-employed who only invoice private individuals, little changes in the short term. Anyone with even a single business customer should know the topic.
What is still to come
involy is an ongoing project. What I miss myself, I build. What others miss, I take as input. Feedback goes directly through the tool or the contact page. No feature request is too small.