Tools that catch errors before you issue an invoice.
Mini-tools we use internally at Cofactu, opened up to the public. 100% in the browser, no server, no storage, no tracking. If they save you 5 minutes a month, they were worth publishing.
NIF · NIE · CIF Validator
Check instantly whether a Spanish tax ID is valid. Official mod-23 algorithm + Orden EHA/451/2008. 100% in your browser, no server.
Open toolSelf-Employed IRPF + VAT Calculator
Estimate your quarterly Modelo 303 (VAT) and Modelo 130 (IRPF installment payment) based on income and expenses. 2026 brackets + annual projection.
Open toolAEAT CSV Checker
Paste an AEAT Secure Verification Code and we'll tell you if the format is correct + a direct link to the official lookup on the AEAT site. No login, no certificate.
Open toolWhat the three share
100% in your browser
The calculation and validation run on your device with JavaScript. We send nothing to any server — you can disconnect from the internet and they keep working.
No signup, no email
We ask for no account, no card, no email. You come in, use it, and leave. None of the tools store or log what you type.
The same engine as Cofactu
These are the mini-tools we use internally: the same algorithm that validates a NIF or calculates the 303 inside the product, opened up to the public.
These mini-tools are handy. Cofactu does the whole job.
The validator, calculator, and CSV checker help in specific moments. Cofactu invoices, signs, sends to AEAT, and files your tax returns. 30 days free, no card required.