Klar

Built to be checked, not trusted.

I am Nicolas Ha, and the engine that reads your mail is open source. Here is why Klar exists, what it will never do, and where it goes next.

Self-funded

No investors. Nothing to sell but the app.

No network access

The free Mac app holds no permission to reach the internet.

Open source engine

AGPLv3 on GitHub. Read the code that reads your mail.

Where this is going

Four products, and the honest status of each.

A spam filter reads everything you receive.

There is no way around that. A filter cannot judge a message it has not read, so the question is where the reading happens. Every big mail provider answers the same way: on our servers. Your correspondence, and the correspondence of everyone who writes to you, ends up with a company they never chose.

The alternative used to be worse, which is why people took the trade. A filter that stayed on your machine could count words and little else. That stopped being true. A multilingual model now fits on a Mac and reads a message in over 100 languages, on the machine the message already sits on. Klar runs that model on your Mac, inside Apple Mail, alongside the header checks that catch a forged sender.

How local-first works

The person on the other end.

Nicolas Ha, founder of Klar

I spent about ten years on large-scale messaging infrastructure and security for regulated systems. That means a news platform doing over a billion views a month, core components for a bank’s licensing, and a message broker I ran alone. Spam is a messaging problem and privacy is a security problem. Those are the two things I have worked on for a decade.

Klar is built in France and bootstrapped. I work on it full time. A technical partner from the messaging and machine learning world covers the early running costs and takes the hard architecture calls with me. No venture money, no board. There is no growth target that would make your inbox worth selling.

What Klar will not do.

Send your mail away to classify it
The free App Store app ships without the network entitlement, and its Mail extension has none either. macOS refuses any connection they try to open. That is a permission the app does not hold, not a policy it promises to follow.
Ask you to sign up
There is no account, so there is nothing of yours to leak. Install it, switch it on in Mail, and it filters. We do not know who you are.
Advertise, or sell anything about you
The app carries no advertising and no automatic telemetry. There is no data business behind Klar, and no version of the plan where there is one.
Charge you for the filter
Klar is free on the Mac App Store and stays free. Klar Plus is the paid companion, and it adds to the free app rather than replacing it.
Ask you to take my word for it
The engine that scores every message is AGPLv3 on GitHub. Read it, build it, check what it does. The demo on the homepage runs the same model against anything you paste into it.

Four products, one rule.

The rule is that the classifier runs on hardware you control, and the one switch that can change it is named below. One of these you can install today. The other three are not there yet.

  1. Klar

    Free on the Mac App Store since July 2026

    The Apple Mail extension. Every message is classified on your Mac, and spam is flagged red for the first 30 days, then moved to Junk.

  2. Klar Plus

    In development

    The paid Mac companion. It shows you every decision, lets you correct it, and learns from your corrections on the device. It also clears the spam already sitting in your mailbox and sorts promotions into their own folder.

  3. Klar for Messages

    Closed TestFlight beta

    An iPhone app that sorts texts from senders you do not know, on the phone. It runs its own small model rather than the email one, which iOS gives a message filter nowhere near enough memory for. This is also the one switch. Check hard cases online is off by default. Turn it on and, for the texts the phone is unsure of, iOS asks our server, carrying the sender and the text. Nothing of either is written down: on arrival the sender becomes a keyed hash and the body a fingerprint, and both expire after 30 days.

  4. Klar Pro

    Built, not yet released

    The same engine filtering on a company’s own mail server, before delivery. The code runs and is tested, and it has no public release yet.

Three things that make a difference.

  • Leave a written review on the Mac App Store. Written reviews are how a small app with no advertising budget gets found.
  • Tell one person who still empties a junk folder by hand.
  • Tell me when Klar gets it wrong. The messages it misses, and the ones it moves by mistake, are what make the next model better.
Report a miss

Thanks for reading this far.

This address goes to my own inbox. I read every message and I answer.

nicolas@klar.im