zlib License
PermissiveSPDX identifier:
ZlibOSI ✓Data updated Sep 26, 2026In plain words
Permissive license: altered source must be marked as altered, the origin must not be misrepresented, and the notice stays in source copies.
Analogy: Borrow the recipe, but if you change it, don't claim it is the original.
Pros
- + Permissive and short
- + Popular for games and native libraries
Cons
- - No patent grant
- - Closed forks are allowed
Well-known projects using it
5 well-known projects in our map use this license.
Permissions
- Commercial use
- Modification
- Distribution
- Private use
Conditions
- Keep copyright notice
- Mark changes
Limitations
- No liability
- No warranty
Extreme scenarios · Code licenses
- A1AllowedA cloud vendor sells your project as a managed service
- A2AllowedSomeone forks it and distributes a closed-source competitor
- A3AllowedEmbedded in a closed-source SaaS backend (not distributed)
- A4AllowedLinked into a closed-source app or firmware and distributed
- A5Blocked by licenseSomeone promotes a modified version with your name or trademark
- A6AllowedSomeone sells unmodified copies
- B1Not addressedA user sues you for patent infringement and keeps using the code
- B2Not addressedA contributor asserts patents on their contributed code
- B3Not addressedA cross-border dispute: governing law and venue
- C1With conditionsYou later relicense or sell commercial licenses (contributors signed no CLA)
- C2AllowedYour code is merged into a GPL-3.0 project
- C3Blocked by licenseYou use a GPL-3.0 dependency and still ship under this license
- C4AllowedThe project is abandoned and someone forks it to continue
- C5Blocked by licenseYou want to block only big companies or competitors
- C6Not addressedKey code was written by an employee and the employer objects
- D1Blocked by licenseSomeone removes copyright or attribution notices
- D2Blocked by licenseSomeone modifies files without marking the changes
- D3AllowedInternal modification, no distribution and no external service
- D4AllowedUsed for military, surveillance or other uses you object to
- D5Not addressedUsed by a sanctioned entity
- D6Not addressedYour code is used to train an AI model
Worst-case radar
- 1Stops free-riding0
- 2Stops closed forks0
- 3Patent protection0
- 4Adoption friction0
- 5Hard to relicense50
Computed from the scenario matrix. Higher means more of that property, not "better".
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Official text
Only the official text is legally binding. We do not translate license texts.
https://spdx.org/licenses/Zlib.html
zlib License
zlib License
This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.