PuTTY redistribution and notice obligations are the conditions the PuTTY licence attaches when the software, or code from it, is passed on to others. PuTTY is distributed under the MIT licence. It grants the rights to use, copy, modify, merge, publish, distribute, sublicense and sell copies, and it has a single condition: the copyright notice and the permission notice must be included in all copies or substantial portions of the software.[1] The developers summarise the only prohibitions as removing their copyright notices or the licence text, and holding them legally responsible if something goes wrong.[3]
Scenarios
| Scenario | Permitted? | What must travel with the copy | Catalog row |
|---|---|---|---|
| Internal installation and use, any number of machines | Yes, free of charge, including commercial use[2] | The unmodified installation already includes LICENCE[1] | Use free of charge |
| Internal software portal, packaged deployment | Yes; permission already granted[3] | Copyright and permission notice | Redistribution needs no separate permission |
| Bundling PuTTY with a commercial product or appliance | Yes; sublicensing and sale are named rights[1] | Copyright and permission notice | Sublicensing and selling copies permitted |
| Modified build or fork | Yes[2] | Copyright notice and licence text in the derived product | Modification permitted with notice retained |
| Reusing PuTTY source in a proprietary program | Yes[2] | Copyright notice and licence text; no source release required | No source-code offer or copyleft obligation |
| Incorporating PuTTY code into a GPL program | Yes; MIT is GPL-compatible[2] | PuTTY notice, alongside the GPL terms of the combined work | PuTTY code may be incorporated into GPL programs |
The notice
The notice to reproduce is the LICENCE text of the release being redistributed. In release 0.85 it begins “PuTTY is copyright 1997-2026 Simon Tatham”. It then names the portions copyright holders, followed by the permission paragraph, the notice condition and the warranty disclaimer.[1] The same text appears in the program’s About box and in Appendix D of the manual.[2] The Windows MSI installer installs the LICENCE file with the executables. Redistributing the installer unchanged therefore carries the notice with it.[1] The standalone executables carry the notice in their About box. Because the licence asks for the notice in “all copies”, a redistributor that repackages the standalone binaries would normally add the LICENCE text to its own package or documentation. That last point is commentary, not a statement by the developers.
The MIT licence has no versions. OSI publishes a single text,[6] and SPDX lets the copyright-holder wording vary within the identifier MIT.[5] PuTTY’s wording, “THE COPYRIGHT HOLDERS” instead of “THE AUTHORS OR COPYRIGHT HOLDERS”, is such a variant. Catalog row: Licence identified as MIT (SPDX), OSI-approved.
Copyleft and linking
The licence contains no copyleft and no source-code obligation. Its only condition concerns the notice.[1] Static or dynamic linking therefore raises no licence distinction for PuTTY code. In practice PuTTY offers no library interface: the SSH and Telnet code is not available as a DLL. The FAQ suggests running Plink as a separate process and talking to it through pipes to make SSH connections from another program.[4] Code taken into a GPL program keeps its MIT notice. The combined program is distributed under the GPL obligations of the rest of the code.[2]
Third-party code with its own notice
The FAQ describes PuTTY as almost completely composed of code written from scratch for PuTTY.[4] One file in the 0.85 source, ssh/crc-attack-detector.c, is the SSH cryptographic attack detector. It is copyright 1998 CORE SDI S.A. and was modified for PuTTY. Its header permits redistribution and use in source and binary forms, with or without modification, provided the copyright notice is retained.[1] CORE SDI S.A. is also listed among the portions copyright holders in LICENCE. Some other files, such as utils/tree234.c, repeat an MIT-style permission notice in their own headers.[1] Catalog row: CORE SDI attack-detector component carries its own notice.
Permission requests and signed documents
No permission is needed to redistribute PuTTY or to reuse its source. The feedback page states “You already have permission”. It recommends, without requiring it, that organisations distributing PuTTY internally or with their own application offer their own first-line support.[3] The developers will not sign permission forms that contain representations or warranties, or any document accepting legal or financial liability.[4] A formal notice of permission would in any case not bind every copyright holder, because many past contributors can no longer be contacted.[4] Catalog row: Developers do not sign indemnities, warranties or individual agreements.
Forks and derivatives
Forks and programs built on PuTTY code, such as KiTTY, ExtraPuTTY and PuTTY Tray, are listed on the developers’ links page with no recommendation implied. Several entries are marked as having no source available.[7] Each is licensed by its own publisher. The PuTTY notice condition applies to the PuTTY portions such a product contains, and the product’s own licence governs the rest. Catalog row: Forks and derived software are outside the project’s control.
Out of scope
This page does not determine the licences of individual forks, the GPL obligations of a combined work, or local encryption and export laws.