Suddenly, we are now hearing about the 'Mojo🔥' language.

Like Julia, it is claimed to favorably compare to languages such as C (open standard) and Python (compatible with GPL); Julia being licensed under MIT.

But what's the mojo license? Shouldn't that be defined somewhere?

At the time of writing this question, I couldn't find the answer either:

The fact that the mojo license is left unsaid in so many places (as it seems) is very surprising and a priori doesn't bode well to be honest. For me, this is sufficient to stay clear from that language. Couldn't they add a license later, one that'd turn out to be proprietary?

  • 3
    The readme states "We plan to open-source Mojo progressively over time, but it's changing very quickly now. We believe that a small, tight-knit group of engineers with a shared vision can move faster than a community effort, so we will continue to incubate it within Modular until it's more complete." Therefore, at the moment, there is no license and you are not supposed to use it. May 9, 2023 at 11:39
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    Who is ‘we’? I have never heard of it. May 11, 2023 at 7:08

2 Answers 2


It seems that as of today, 2023-05-09, the only way to "use" Mojo is via the developer's playground:

The Mojo standard library, compiler, and runtime are not available for local development yet

With nothing being distributed, there's no need for a license at this time - personally though I would be very wary of investing time in a language where there isn't a freely available reference implementation; too much risk of a "bait and switch" where I suddenly have to pay $$$ to do what I want to do.

  • 13
    Additionally, the implicit claim that an open source license means to let go of developing it in a 'tight-knit group of engineers' is of course bogus. Both can be very well true at the same time. It just means they don't understand open source, but rather see it as free labour or cheap maintenance and testing May 9, 2023 at 11:45
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    I'm also a bit suspicious of a language where the preferred source filename extension is an emoji!
    – MadHatter
    May 9, 2023 at 12:06
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    I see, thanks; it's even less inviting than I thought. Also: I fully agree with your comment about time investment (the original wording of my question was harsher). Beware.
    – Alex
    May 9, 2023 at 12:23
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    @planetmaker They may (as many people do) incorrectly equate "open source" with a "community development" model. May 10, 2023 at 16:41
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    @planetmaker: The most extreme example of this probably being SQLite, which is developed by three people, does not accept patches, and is in the public domain.
    – Kevin
    May 12, 2023 at 17:23

According to goldiegadde at issue #84:

Mojo is not opensourced yet, see docs.modular.com/mojo/faq for further details.

From the FAQ:

Will Mojo be open-sourced?

Yes, we expect that Mojo will be open-sourced. However, Mojo is still young, so we will continue to incubate it within Modular until more of its internal architecture is fleshed out. We don’t have an established plan for open-sourcing yet.

Why not develop Mojo in the open from the beginning?

Mojo is a big project and has several architectural differences from previous languages. We believe a tight-knit group of engineers with a common vision can move faster than a community effort. This development approach is also well-established from other projects that are now open source (such as LLVM, Clang, Swift, MLIR, etc.).

So no license at the moment.

  • 1
    Looking at the issue you linked, this is first time I've seen entire sentences (and clauses) being copy-pasted without modification from Stack Exchange to GitHub without referring to the original discussion. I know Stack Exchange questions and answers are CC-BY-SA. 'BY' stands for attribution, and I find it quite extraordinary that the poster of that issue goes as far as to moreover copy-paste from Philip Kendall's answer later on, without making any reference to the discussion here.
    – Alex
    May 12, 2023 at 16:20
  • Oh, hats off, Alex! In a metaverse not so far, may your humble mound of SO karma equip you with divine powers to obliterate such truly 'despicable' conduct on GitHub. May 18, 2023 at 11:19
  • Topics in this Stack Exchange community precisely concern open licenses. I'm afraid you've just created an account here merely to show everyone that you miss the point completely Praveen Kulkarni.
    – Alex
    Jun 14, 2023 at 9:41
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    Might be worth noting that now, as of 2023-09-08 the FAQ has changed the first phrase from "Yes, we expect that Mojo will be open-sourced" -> "Over time we expect to open-source core parts of Mojo, such as the standard library."
    – txomon
    Sep 8, 2023 at 15:22
  • Thanks @txomon. It's very interesting that there's already been changes in their communication, strongly limiting the scope of their would-be openness. The sentence you quote was still in the FAQ until at least 2023-11-28 (as can be seen in web archives); they now remain vague instead. Yet another very big red flag.
    – Alex
    Feb 23 at 9:07

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