ISC License Explained — Plain English Guide (Simplified MIT & Commercial Use)

The ISC License is a permissive open-source license functionally identical to the MIT License but with simpler, more streamlined language — it lets you do almost anything with the code including commercial use, with the only requirement being to keep the copyright notice. It’s the default license for OpenBSD and is used by thousands of npm packages including popular tools like semver, node-fetch, and ini.

What You’ll Learn

By the end of this guide, you’ll understand how the ISC License differs from MIT, whether you can use ISC code in commercial products, why OpenBSD and npm developers prefer it, and how to decide between ISC and other permissive licenses.

Why It Matters

The ISC License is one of the simplest open-source licenses ever written — shorter even than MIT. It eliminates what some consider unnecessary legal language while preserving the same permissive rights. If you’ve ever used an npm package, you’ve almost certainly used ISC-licensed code. Understanding ISC helps you choose the right license for your own projects and know your obligations when using ISC dependencies.

Real-World Use

Your startup installs node-fetch (ISC-licensed) to make HTTP requests from your Node.js backend. Your app makes millions in revenue. Under ISC, you owe the author nothing except keeping their copyright notice in your distribution. You don’t need to pay, register, open-source your code, or ask permission. The ISC License is that simple.

Quick Reference

What the ISC License Actually Says

The ISC License is the shortest open-source license approved by both the Open Source Initiative (OSI) and the Free Software Foundation (FSF). Here is the complete text:

ISC License

Copyright (c) 2024 [Copyright Holder]

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES...

ISC vs MIT: The Language Difference

The ISC replaces MIT’s enumerated list of rights (“use, copy, modify, merge, publish, distribute, sublicense, and/or sell”) with the simpler “use, copy, modify, and/or distribute this software for any purpose.” The phrase “for any purpose” does all the work — it implicitly includes commercial use, selling, and sublicensing.

Why ISC Was Created

The ISC License was written by the Internet Systems Consortium (ISC), the organization behind BIND (the dominant DNS server software). They wanted a license that was:

1. As permissive as possible
2. Shorter than MIT
3. Free of what they considered unnecessary legal boilerplate
4. Compliant with the Berne Convention copyright standards

OpenBSD adopted it as their preferred license, and from there it spread through the open-source ecosystem.

Can I Use ISC Code in Commercial Products?

Yes, absolutely — same as MIT. The ISC License places no restrictions on commercial use. You can:

• Use ISC code in proprietary commercial products
• Sell products containing ISC code
• Modify ISC code and keep modifications private
• Include ISC code in SaaS products
• Build a business around ISC-licensed software

The Only Requirement

Keep the copyright notice and permission notice in all copies of the software. This means:

• Don’t remove the copyright header from source files
• If you distribute the code in binary form, include the notice in documentation or a LICENSE file
• If you use an ISC npm package, the notice travels with the package — you typically don’t need to add anything

Real-World Projects Using ISC

Why npm Package Authors Love ISC

The ISC License is extremely popular in the npm ecosystem for several reasons:

1. Shortest possible license text — just paste it into your LICENSE file and you’re done
2. Covers everything MIT covers — no functional difference in practice
3. No “deal” language — ISC uses “use, copy, modify, and/or distribute” instead of MIT’s “deal in the Software without restriction”
4. OpenBSD pedigree — security-focused developers trust it
5. OSI and FSF approved — meets all open-source definition requirements

ISC vs MIT vs BSD 2-Clause

All three are functionally equivalent. Here are the nuanced differences:

Bottom line: Choose ISC if you want the shortest possible license text. Choose MIT if you want the most widely recognized license. Choose BSD 2-Clause if you prefer more formal legal language.

Common Misconceptions

“ISC is not as legally sound as MIT”

Both are OSI-approved and FSF-approved open-source licenses. ISC has been tested in practice for decades. It’s the license used by OpenSSH, OpenBSD, and BIND — projects that have stringent legal requirements. It’s every bit as enforceable as MIT.

“ISC doesn’t allow selling software”

The ISC says “for any purpose with or without fee.” “Any purpose” includes selling. “With or without fee” explicitly covers the case where you charge money. Selling is permitted.

“ISC is only for C projects and OpenBSD”

ISC originated in the OpenBSD ecosystem, but it’s now widely used across all programming languages. The npm ecosystem has thousands of ISC packages. Nothing in the license restricts it to any platform or language.

“I need to include the full ISC text in every file”

Not required. The license says the notice must appear “in all copies.” For source distribution, this typically means a LICENSE file. File headers are best practice but not legally required.

“ISC doesn’t have a warranty disclaimer”

It does. The ISC License includes a standard no-warranty clause: “THE SOFTWARE IS PROVIDED ‘AS IS’ AND THE AUTHOR DISCLAIMS ALL WARRANTIES.” This is functionally equivalent to MIT’s disclaimer.

When to Choose ISC

Choose ISC for your own projects when:

• You want the shortest possible open-source license
• You’re contributing to the OpenBSD ecosystem
• You’re publishing an npm package (many npm devs prefer ISC)
• You want permissive licensing and don’t need patent protection
• You appreciate minimalist legal language

Avoid ISC when:

• You want the most widely recognized license (choose MIT)
• You need a patent grant (choose Apache License 2.0)
• You want copyleft protection (choose GNU GPL or GNU LGPL)
• Your corporate legal team prefers the more verbose license they’re familiar with
• Trademark protection matters (Apache License 2.0 has explicit trademark clauses)

FAQ

License Simplicity Ranking

graph LR
    A[ISC ~140 words] --> B[MIT ~200 words]
    B --> C[BSD 2-Clause ~200 words]
    C --> D[Apache 2.0 ~500+ words]
    D --> E[GPLv3 ~6000+ words]
    style A fill:#90EE90
    style B fill:#90EE90
    style C fill:#90EE90
    style D fill:#FFD700
    style E fill:#FFA500

Practice Questions

1. You build a commercial SaaS platform using the node-fetch npm package (ISC). Do you need to release your platform’s source code? No. ISC is a permissive license with no copyleft requirement. Your SaaS code stays proprietary.

2. You copy an ISC-licensed function from an OpenBSD utility into your mobile app. What must you include? The copyright notice from the original source file. A LICENSE file with the ISC text is sufficient compliance.

3. Your company rewrites an ISC-licensed library from C to Rust, modifying the design significantly. Is the Rust version under ISC too? If it’s a derivative work (substantially based on the original), the copyright notice must stay, and the ISC license covers the copied work. Your original additions can be under any license.

4. You find a bug in an ISC library and fix it. Do you have to contribute the fix back? No — ISC has no obligation to share modifications. You can keep the fix private. Contributing back is good practice but not required.

5. Which license is shorter — ISC or MIT? ISC — approximately 140 words versus MIT’s 200 words. ISC drops “deal in the Software without restriction” for “use, copy, modify, and/or distribute this software for any purpose,” cutting 60 words while preserving the same legal effect.

Mini Project: License Comparison

1. Download the full text of ISC, MIT, and BSD 2-Clause licenses
2. Create a table comparing:
   • Word count
   • Specific rights mentioned (use, copy, modify, distribute, sell, sublicense)
   • Warranty disclaimer text
3. Replace the copyright holder placeholder in each with your own name
4. Decide which one you’d use for your next open-source project and write a one-paragraph justification
5. Check how many of your npm dependencies use ISC vs MIT licenses using npx license-checker

Challenge: Look at the OpenBSD project’s licensing policy. Read why they prefer ISC over MIT. Then look at the npm package semver — one of the most downloaded packages, licensed under ISC. Consider: does the license of a foundational package like semver affect the broader ecosystem? Write a short analysis.

Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro. This guide is for educational purposes and does not constitute legal advice. Consult an attorney for specific licensing questions.