Cobalt vs Koober: which French book summary app should you choose?

Let's say it upfront: this article is published on the Cobalt blog. We are both judge and contestant here, and you deserve to know that before reading a single line. But a comparison is only useful if it is honest: Koober is a serious service, a pioneer of French-language book summaries, and caricaturing it would help no one, starting with us.

If you are looking for a French-language book summary app, the two names that come up most often are Koober and Cobalt. Here is what they have in common, what sets them apart, and above all how to choose based on the way you learn.

Koober: the French pioneer of book summaries

Koober offers koobs, condensed versions of non-fiction books (business, personal development, science, history) that you can read or listen to in about twenty minutes. Available on iOS and Android, the app established itself as one of the first French-speaking alternatives to Blinkist. The format targets French-speaking professionals, students and curious minds who want to extract the essentials of a book without spending several hours on it.

Its website mentions a library of several hundred koobs, and reviews published in 2026 report more than 1,500 titles in the catalogue, mostly in French, with dozens of new summaries every month. As far as we know, it is the largest French-language summary catalogue on the market. The writing quality is judged decent by most reviews, although some readers report occasional typos in the koobs.

When it comes to formats, Koober plays on both fronts: every koob exists in a text version and an audio version. The app has in fact largely repositioned itself around listening, to the point of presenting itself on the app stores as a 'book podcasts' app. For commutes and everyday chores, that is a real strength.

Cobalt: summaries designed for retention

Cobalt is also a French book summary app, available on iOS and Android, but with a different philosophy: rather than aiming for the largest possible catalogue, it crafts every summary as a learning object. A Cobalt summary takes 8 minutes on average to read, broken down into key concepts with the strongest ideas highlighted. The goal is not to replace reading, but to make sure that ten minutes of attention leave a lasting trace.

Its most distinctive feature is the adjustable summary length: a control lets you expand or shorten the text in real time, depending on how much time you have and how much detail you want. Five minutes before a meeting or twenty minutes on the train are not the same summary, and that is exactly the point.

Another structural difference: part of the Cobalt catalogue is freely accessible on the web, with no sign-up. Around forty summaries (Atomic Habits, The 7 Habits of Highly Effective People, Thinking, Fast and Slow...) can be read for free in a browser, which lets you judge the quality before installing anything.

Catalogue: depth versus selection

On volume, Koober wins hands down. If your goal is to browse as many titles as possible and pick whatever catches your eye, its catalogue is better equipped. Cobalt, on the contrary, embraces a tight, selective catalogue focused on reference books about habits, productivity, psychology and business, expanded regularly. So the real question is not 'who has more titles?' but 'what do I want: to skim everything, or to retain the essentials of the books that matter?' In other words, Koober feels like a media library you wander through, Cobalt like a bedside shelf where every book was chosen to be read again.

Formats: audio versus interactive text

Koober favours listening, Cobalt favours active reading. This is not a detail: listening to a summary while doing something else is comfortable, but highlighting, adjusting the length and re-reading a concept demands more attention, which helps retention. It is the same gap as between a podcast and a revision sheet: both have their place, but they do not produce the same memory a week later. We covered what summaries are really worth for learning in a dedicated article: https://www.cobaltapp.io/fr/blog/pourquoi-lire-des-resumes

Pricing: two different logics

According to the prices displayed on Koober's website in July 2026, the subscription costs 7.99 euros per month, or about 6.70 euros per month with annual billing, and the free plan gives access to one koob per week, chosen by the platform. These prices may change: check their website for up-to-date rates.

Cobalt works differently: the summaries published on its website are free, with no weekly limit and no account required. The app offers a Premium plan (all summaries, adjustable length, offline mode, personalised recommendations) with a 7-day free trial; prices are displayed directly in the app. This free web entry point is rare on the French-speaking market: it lets you judge the real quality of the summaries with no commitment, even before trying the app.

The comparison table

Verdict: two apps, two needs

Choose Koober if you want the widest possible choice of French-language summaries and audio is your main format: it is an established service with a steady publishing pace and real expertise in condensed audio content.

Choose Cobalt if your priority is to remember what you read: highlighted concepts, length adjustable in real time, and summaries you can test for free on the web before installing anything. Fewer titles, but an experience built so that ideas stick.

We applied the same framework to the English-speaking giant of the sector in our comparison between Cobalt and Blinkist: https://www.cobaltapp.io/fr/blog/cobalt-vs-blinkist-application-resumes-livres

The simplest thing is to make up your own mind: our summaries are freely available here https://www.cobaltapp.io/fr/resumes and the app is a free download on iOS and Android here https://www.cobaltapp.io/download . And if Cobalt does not fit the way you learn, Koober remains a safe bet for French-language summaries: that too is what an honest comparison means.