Brazilian developers have leaned on 4devs since 2012 to generate valid CPF, CNPJ, RG and CNH numbers for testing, and the site now covers dozens of small tools in one menu. This page walks through what 4devs actually does, which tools matter most for QA work, and how its new alphanumeric CNPJ option fits the Receita Federal change that began on 31 July 2026. You’ll also see where its output stops being useful, because a number that passes a check digit is not a real person. By the end, you’ll know exactly which generators to reach for and which checks still need your own code.
Short Answer
4devs is a free Brazilian website, running since 2012, that generates and validates test data such as CPF, CNPJ, RG, CNH and fake people profiles. Developers use it to fill forms and test validation rules, and since mid-2026 its CNPJ generator also produces the new alphanumeric format.
What the Site Actually Is
The site is a collection of browser-based utilities built mostly for Brazilian programmers, analysts and testers, and its footer credits the company 7graus with a copyright range that starts in 2012. The top menu splits into Computação and Matemática, and the Computação side alone groups generators, validators, SEO helpers, string functions, network lookups, encoders and reference tables. Nothing needs installing, so a tester can open a page, click once and paste the result straight into a form.
What sets it apart from a generic random-data site is how thoroughly Brazilian it is. Most of the documents it generates, including CPF, CNPJ, RG, CNH, PIS/PASEP, RENAVAM, voter registration and state registration numbers, only exist in Brazil, so a developer working on a local system rarely finds a ready-made generator for them anywhere else. Each generator has a matching validator, which makes the pairing useful for checking your own code against a second opinion.
The Generators Most Testers Reach For
Nobody uses all of it. In practice a handful of pages cover most daily work, and these are the ones worth bookmarking.
- The CPF generator, with a switch for dotted or plain output and a dropdown for the state of origin.
- The CNPJ generator, now with a choice between numeric and alphanumeric format.
- The person generator, which returns a full profile with name, RG, CPF, postal code, address and phone in one click.
- The company generator, which bundles a name, CNPJ, state registration and postal code.
- Credit card number and bank account generators, each with its own validator.
The person and company generators are the real time savers, because one click fills a whole registration form with matching fields instead of five separate trips between pages. I’d start there for any sign-up flow and drop down to the single-document pages only when you need to control one detail, like the CPF’s state.
The Smaller Utilities People Forget
Beyond documents, the menu holds a surprising amount of everyday tooling. String helpers count characters, words and lines, strip accents, flip case, split text and spell out numbers in Portuguese, while the encoder section covers Base64, MD5, SHA1, CRC32, URL encoding and QR codes. Network pages report your IP, browser and operating system, and reference pages offer an ASCII table and a color picker.
On the labor side, there’s a vacation pay calculator and a contract termination calculator, which are unusual company for a developer toolbox. Treat those as quick estimates, since real payouts depend on contract details and collective agreements that a simple form can’t see.
How the CPF Generator Builds a Number
A CPF has 11 digits, and only nine of them are free. The last two are check digits calculated from the first nine with a modulo 11 formula, which is why a typo in a real CPF usually gets caught without any database lookup. The ninth digit also marks the fiscal region where the number was first registered, such as 8 for São Paulo and 7 for Rio de Janeiro and Espírito Santo, and that’s what the state-of-origin dropdown lines up with. The structure is well documented, so the Wikipedia entry on the CPF number is a fair place to check the layout yourself.
Simple arithmetic shows the limit of that design. Nine free digits give one billion possible bases, and each base gets exactly one pair of check digits, so the number space is smaller than it looks. Sequences with every digit identical, such as 111.111.111-11, technically pass the modulo test but are rejected by convention, which means any decent generator has to skip them and your own validator should too.
The Alphanumeric CNPJ Change
This is the development that makes the site matter in 2026. On 31 July the Receita Federal generated the first alphanumeric CNPJ, a 14-character identifier that mixes letters and numbers. The agency’s own question-and-answer document on the alphanumeric format explains how the new structure works and how the check digits are calculated.
Existing numbers stay valid, and purely numeric ones can still be issued, since only about 69 million of the 99,999,999 possible numeric root combinations had been used according to the agency’s announcement. So both formats will coexist, and every system that stores a CNPJ has to accept both. The tax authority also published simulated alphanumeric CNPJs for testing in nine states on 9 July 2026, which tells you how seriously it expects integrations to be checked.
The CNPJ page here now includes a format selector with a numeric option and an alphanumeric one labeled with the IN RFB 2.229/2024 rule. That gives testers a quick way to produce letter-based values without writing the check digit routine first. Bugs tend to hide in boring places, so expect a form that strips non-digit characters to quietly mangle a letter, a numeric database column to reject the value, and an input mask to block typing it at all. Push both formats through every field, export and third-party integration that touches a CNPJ.
The Mistake That Makes Generated CPFs Risky
Plenty of people assume that a generated CPF is fake and therefore harmless. It’s valid by arithmetic only, which is a different thing from being invented. With roughly 210 million residents in Brazil and only one billion possible bases, a randomly generated CPF has a real chance of matching a living person.
The confusion comes from the word “valid.” In a tool, it means the check digits agree, but in everyday speech it means the person exists and the registration is regular. A check digit can’t prove either, and confirming a real status means querying the Receita Federal, which no generator ever does.
The practical rule is simple. Use generated documents in test and staging environments only, never in production sign-ups or real transactions, and remember that the site itself puts responsibility for misuse on the user. The upside is real too, since synthetic data keeps actual customers’ records out of your test databases, which fits the spirit of Brazil’s data protection law.
Where It Falls Short
The site is built for clicking, not for automating. The generator pages promote a REST API for backend use, and an unofficial npm package called 4devs exists that wraps the site’s pages, but that means your test suite depends on a third-party website staying online and unchanged. For continuous integration I’d generate documents locally with a small library and keep the website for manual exploring.
Speed and design are the other common complaints. One developer on TabNews built a competing tool called GeraFácil because they wanted a faster, more pleasant version of the same idea, and several other open source generators have appeared for similar reasons. If you like keeping a short list of free browser utilities close at hand, a few more plain-language rundowns of useful online tools are worth a look as you build it.
Conclusion
For one-off testing, 4devs remains one of the quickest ways to get a valid CPF, CNPJ or full test profile without installing anything. The thing to do this week is open its CNPJ generator, switch to the alphanumeric format, and push those values through every form and import in your system. Anything that breaks now will break for a real customer later. Keep generated documents out of production, and move repetitive test runs to a local generator so your pipeline never depends on a website.
FAQ
Is 4devs free to use?
The generators I checked open without an account, and the site carries ads. It also promotes a REST API for backend use, so check the terms on that page before building anything on it.
Who runs 4devs?
The footer credits 7graus, with a copyright range of 2012 to 2026. The site’s About and Terms of Use pages are linked from the same footer.
Does the CNPJ generator support the new letter-based format?
Yes. The page offers a format selector with a numeric option and an alphanumeric option labeled with IN RFB 2.229/2024.
Does a generated CPF prove the person exists?
No. It only means the two check digits match the first nine, so the number may belong to nobody or to a real person. Real status can only be confirmed with the Receita Federal.
Can I use generated documents to sign up on real websites?
You shouldn’t. The site states that misuse of generated data is the user’s responsibility, and the numbers are meant for testing software in development.