Sooner or later, every developer runs into The License Question. You shipped something to GitHub, GitHub asked you to pick a license, and you scrolled the dropdown — MIT, Apache, GPL, AGPL, BUSL, MPL, ISC, Unlicense, "Other" — and picked whatever sounded least scary. That's how I did it. That's also how I ended up rewriting my LICENSE file three weeks later.
Licenses are a dark forest for devs. We don't read legal docs, nothing in our day-to-day teaches us when each one matters, and most online advice is either a wall of legalese or someone's religious argument. Here's the version I wish someone had given me: a tour of the five licenses you'll actually meet, the mistakes that bite, and what changing my license did to my project's discoverability in the real world.
What a license actually does
By default, your code is "all rights reserved." That sounds like the default-est thing possible — but it means no one can legally copy, fork, run, or modify your code without your written permission. Sticking your project on a public GitHub repo doesn't change that. A license is the contract you write with the world that relaxes the default.
The question you're answering when you pick one: how much can people do with this, and what do you get back?
The five you'll actually meet
MIT. "Use my code. Just keep my name in the file. Don't sue me." Three paragraphs long. Maximum adoption, zero protection. Most of the JavaScript ecosystem runs on MIT, and most of those projects don't have a monetization plan, which is exactly why it works for them.
Apache 2.0. Like MIT, but explicitly grants patent rights from contributors to users. That sounds boring until you realize half the tech world is built on patented stuff and silently assumes nobody will sue. Apache is the grown-up version of MIT — same vibe, fewer landmines.
GPL-3.0. "Modify and distribute my code? Your modifications are also GPL." This is copyleft. It infects everything downstream, which is why corporate lawyers hate it and Linux thrives on it (the kernel is GPL-2). Companies can't quietly fold GPL code into their proprietary stack — the license would force the whole stack open.
AGPL-3.0. GPL with a single, brutal addition: §13. If you modify the code and run it as a network service — a SaaS, a hosted dashboard, anything users hit over the network — you have to publish your modifications. This closes the loophole that GPL leaves open, where a company can fork, modify privately, and host the modified version. AGPL says: nope, your fork has to be public the moment users touch it.
BUSL-1.1. Not actually open source by the OSI's definition — it's "source-available." You can read the code, fork it, run it for yourself; you can't sell it as a hosted commercial service competing with the original author. After four years it auto-converts to a real OSI license (usually Apache). Sentry, MariaDB, CockroachDB — all BUSL. It's a defensive license aimed at the "AWS forks our project and undercuts us on hosting" scenario.
(There's also MPL-2.0 — file-level copyleft, used by Firefox. A reasonable middle ground if MIT feels too loose and AGPL too aggressive. Not your most-likely first encounter, so I'm leaving it as a footnote.)
Mistakes I see all the time
Picking MIT for a thing you might monetize. The most expensive mistake. MIT lets a competitor fork your work, polish it, host it, and out-market you — with zero recourse. Fine for a library nobody wants to commercialize. Bad for a product.
Copying BUSL because Sentry uses BUSL. Different threat models. Sentry has hyperscaler-competition risk; you have nobody-knows-you-exist risk. BUSL solves a problem you don't have, while costing you contributor goodwill, awesome-list eligibility, and brand clarity. I learned this one personally.
Slapping GPL or AGPL on a library. Copyleft on a library is contagious — anything that links to it inherits your license. Devs see it and walk away because they can't safely use your code in their proprietary or differently-licensed project. Libraries should almost always be MIT or Apache.
No license at all. The silent killer. "All rights reserved" is the default, so a public repo with no LICENSE file is technically a public repo nobody can legally use. You're sending the message: here's my code, but also nobody can touch it. If you want adoption, ship a license.
Picking the most "open" license to look generous. MIT looks generous. It's also the easiest license to regret. The right question isn't "how open should I look" — it's "what business model do I want to keep available?" Be honest with yourself before you optimize for image.
What changing the license actually changed
I shipped .
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